首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5013篇
  免费   475篇
  国内免费   6篇
耳鼻咽喉   46篇
儿科学   99篇
妇产科学   126篇
基础医学   749篇
口腔科学   234篇
临床医学   625篇
内科学   972篇
皮肤病学   43篇
神经病学   371篇
特种医学   183篇
外科学   605篇
综合类   104篇
一般理论   7篇
预防医学   550篇
眼科学   36篇
药学   423篇
中国医学   8篇
肿瘤学   313篇
  2021年   77篇
  2020年   55篇
  2019年   77篇
  2018年   88篇
  2017年   74篇
  2016年   74篇
  2015年   85篇
  2014年   106篇
  2013年   145篇
  2012年   246篇
  2011年   256篇
  2010年   123篇
  2009年   117篇
  2008年   218篇
  2007年   216篇
  2006年   252篇
  2005年   215篇
  2004年   211篇
  2003年   172篇
  2002年   181篇
  2001年   176篇
  2000年   189篇
  1999年   125篇
  1998年   67篇
  1997年   59篇
  1996年   46篇
  1995年   60篇
  1994年   56篇
  1993年   50篇
  1992年   107篇
  1991年   124篇
  1990年   104篇
  1989年   84篇
  1988年   57篇
  1987年   86篇
  1986年   96篇
  1985年   82篇
  1984年   65篇
  1983年   62篇
  1982年   39篇
  1981年   33篇
  1979年   62篇
  1978年   45篇
  1977年   42篇
  1976年   33篇
  1975年   41篇
  1974年   48篇
  1973年   34篇
  1972年   45篇
  1969年   41篇
排序方式: 共有5494条查询结果,搜索用时 46 毫秒
61.
Y chromosome deletions encompassing the AZFc region have been reported in 13% of azoospermic men and 7% of severely oligozoospermic men. We examined the impact of these Y deletions on the severity of testicular defects in 51 azoospermic men undergoing intracytoplasmic sperm injection (ICSI) after testicular sperm extraction (TESE) and 30 men with severe oligozoospermia undergoing ICSI after ejaculation of spermatozoa. In addition, five azoospermic patients shown previously to have Y chromosome deletions underwent histological evaluation of their previously obtained testis biopsy specimens. A further 27 azoospermic men underwent TESE-ICSI, but not Y chromosome DNA testing. Ten of 51 azoospermic men (20%) who underwent TESE-ICSI and Y-DNA testing were found to be deleted for portions of the Y chromosome AZFc region. Of these 10, five had spermatozoa retrievable from the testis, and in two cases the wives became pregnant. Of the 41 azoospermic men with no Y chromosome deletion, 22 (54%) had spermatozoa retrievable from the testis, and in 12 cases (29%) the wives became pregnant. Four of 30 (13%) severely oligozoospermic patients were found to be deleted for AZFc and in three (75%) of these pregnancy was achieved. The other 26 severely oligozoospermic couples who had no AZFc deletions underwent ICSI, and 12 (46%) have an ongoing or delivered pregnancy. The embryo implantation rate was not significantly different for azoospermic (22%), oligozoospermic (16%), Y-deleted (14%) or Y-intact (18%) men. Of the total of 19 infertile men who had Y chromosome deletions, 14 had deletions within Y chromosome intervals 6D-6F, in the AZFc region. Twelve of those 14 had some spermatozoa (however few in number) in the ejaculate or testis. Five of the Y-deleted men had deletions that extended more proximally on the Y chromosome, and in none of these could any spermatozoa be observed in either ejaculate or testis. These results support the concept that, in azoospermic or oligozoospermic men with Y chromosome deletions limited to intervals 6D-6F (AZFc), there are generally very small numbers of testicular or ejaculated spermatozoa. Larger Y deletions, including and extending beyond the AZFc region and encompassing more Y genes, tend to be associated with a total absence of testicular spermatozoa. In those cases where spermatozoa were retrieved, the presence of Y deletions had no obvious impact on fertilization or pregnancy rate.   相似文献   
62.
In the histologic grading of invasive breast cancer with the Nottingham modification of the Scarff-Bloom-Richardson grading scheme (NSBR), it has been found that when pathologists disagree, they tend not to disagree by much. However, if tumor grade is to be used as an important parameter in making treatment decisions, then even this generally small degree of pathologist variability in assessing grade needs to be correlated with patient outcome. Findings from the Nottingham/Tenovus Primary Breast Cancer Study were used for patient outcome data. Kaplan-Meier survival curves were constructed for NSBR scores grouped according to the level at which pathologists tend to agree in assessing grade, from a reproducibility perspective. For example, if a given tumor were assessed by several pathologists as having either an NSBR score of 5 or 6, then what is the correct score--the intermediate-grade Score 6 assessments or the low-grade Score 5 assessments? By "regrouping" the Nottingham outcome data such that data from patients with Score 5 tumors are grouped with patients having Score 6 tumors (a 5-6 group), then the level in which the pathologists agreed with each other (that the tumor was either score 5 or 6) is better matched with patient outcome. In response to the above example, it was not surprising to find that patients with Score 5-6 tumors had a probability of survival between the established low and intermediate NSBR final combined grades. However, it is the discussion of this approach that highlights that optimal use of grading requires awareness of the level of pathologist agreement and understanding the value of pathologists' reaching consensus in assessments. Also, knowledge of possible clinical decision thresholds can help in providing relevant interpretations of grading results.  相似文献   
63.
The aim of the study was to determine whether different programmes of exercise influence adoptive monophasic experimental auto-immune encephalomyelitis (adoptive EAE), a paralytic disease mediated by T-cells. Adoptive EAE was induced by the transfer of activated encephalitogenic T-lymphocytes into syngeneic recipients (Lewis rats, n = 85) and its development was followed by two independent observers. The results showed that 2 days of severe exercise (250 and 300 min) performed after the adoptive transfer of EAE slightly delayed the onset of the disease (P < 0.008) and the day of its maximal severity (P < 0.016) without affecting the overall severity of the disease. When this programme of exercise was performed before the cell transfer, it had no effect (P > 0.05). Two more moderate exercise programmes (5 × 120 min of running at constant speed or 5 × 60 min of running at variable speed, 5 consecutive days) performed between the adoptive transfer and the onset of the disease did not modify the development of the clinical signs of adoptive EAE (P >0.05). These results showed that severe exercise slightly influenced the effector phase of monophasic EAE and confirmed that physical exercise performed before the onset of experimental auto-immune diseases did not exacerbate the clinical signs.  相似文献   
64.
Several techniques have been developed for protein immunolocalization in meiotic cells. However, most of them include treatments that lead to cell disruption and are only suitable for prophase-I cells. We describe a novel squash procedure of cell preparation for protein immunolabelling of different meiotic stages. This procedure is an alternative to both cryosectioning and whole spreading procedures. We present results obtained in mouse spermatocytes with three different antibodies: the MPM-2 mAb against mitotic phosphoepitopes, an anticentromere serum and a polyclonal serum against the SCP3 protein of the axial elements and lateral elements of the synaptonemal complex. The procedure was tested for single and double immunolabelling. With this technique a large number of cells at different meiotic stages can be analysed. Cell stages are easily identified and cell and chromosome structures are preserved. Thus, it allows the study of chromosome behaviour and the relations hips between the different structural elements of the cell throughout meiotic divisions. Our procedure is also suitable for three-dimensional (3D) analyses and proved to be reliable in a wide range of systems including insects and mammals. In addition, the procedure may be interesting to obtain a rapid immunological diagnosis.  相似文献   
65.
Two experiments tested the hypothesis that the deficits in conditional discrimination learning produced by ibotenic acid-induced lesions of the ventral pallidum and substantia innominata are produced by loss of the magnocellular cholinergic cells in the nucleus basalis and adjacent regions. Experiment 1 replicated the previously reported deficit in conditional learning produced by ibotenate-induced lesions of the ventral pallidum/substantia innominata, but failed to demonstrate any restoration of learning by a subchronic regimen of the acetylcholinesterase inhibitor physostigmine sufficient to produce significant (30%), but equivalent, degrees of inhibition in the frontal cortex of ventral pallidum/substantia innominata-lesioned or sham-operated rats. Experiment 2 examined the effects of quisqualic acid-induced lesions of the ventral pallidum/substantia innominata. According to most of the measures of learning employed, the quisqualic acid-induced lesion of the ventral pallidum/substantia innominata failed to impair conditional learning, even though the quisqualate-induced lesion produced greater degrees of cholinergic neuron destruction than the ibotenate-induced lesion, as measured in terms of reductions in cortical choline acetyltransferase activity (44% vs 27%). Although consideration of individual data suggested that very high (60%) levels of choline acetyltransferase reduction in Experiment 2 might have detrimental effects of conditional learning, the overall failure of the quisqualate-induced lesions of the ventral pallidum/substantia innominata to impair learning is to be contrasted with the significant behavioural effects of ibotenate-induced lesions. Histological and immunocytochemical analysis showed that the quisqualate-induced lesion, unlike that produced by ibotenate, tended to produce less damage to the overlying dorsal globus pallidus and to parvocellular neurons of the ventral pallidum/substantia innominata, thus implicating these nonspecific effects of ibotenate-induced lesions in their behavioural effects. The present results question previous interpretations of the behavioural effects of ibotenate-induced lesions of the ventral pallidum/substantia innominata in terms of damage inflicted on the cortically-projecting cholinergic cells of the nucleus basalis, and suggest that quisqualic acid, although also nonspecific in its excitotoxic effects, is nevertheless more selective for producing damage to cholinergic neurons in the ventral pallidum/substantia innominata than ibotenic acid.  相似文献   
66.
67.
68.
Porphyromonas gingivalis is a suspected pathogen in rapidly progressive periodontitis (RPP). We have determined the anti-P. gingivalis serum immunoglobulin G (IgG) isotype response and avidity and the subclass titer distributions for 30 RPP patients and 30 age-, sex-, and race-matched healthy subjects by using enzyme-linked immunosorbent assay technology. Patients and control subjects were classified as seropositive if their total IgG response to P. gingivalis was twofold or more than the median response in healthy subjects. The predominant antibody responses for both patients and healthy subjects were IgG2 and IgG3, with a subclass order of IgG2 greater than IgG3 greater than IgG1 greater than IgG4. The avidity of the IgG response was highest for the seropositive healthy subjects and was no different between seronegative and seropositive RPP patients. The subclass antibody responses did not depend on gender, and there were no correlations between titer, avidity, or subclass with disease severity in the RPP patients as measured by pocket depth or bone loss on dental X rays. The seronegative RPP patients exhibited antibody responses that were greater than the responses of seronegative healthy subjects for all four subclasses, while the seropositive RPP patients had higher IgG1 and IgG4 levels than seropositive healthy subjects. These findings are consistent with the hypothesis that both carbohydrate and protein antigens are important in the IgG response to P. gingivalis. The relative predominance of IgG2, a subclass which lacks strong complement fixation and opsonic properties, and the low avidity of patient anti-P. gingivalis IgG antibodies suggest that humoral responsiveness to infection with P. gingivalis may be ineffective in clearing this organism.  相似文献   
69.
A morphologic investigation of ependyma over gray matter (caudate nucleus) and over periventricular white matter (tapetum) of the rabbit lateral ventricle was performed four months after the induction of experimental hydrocephalus. Ependymal cells over the caudate nucleus are not modified by hydrocephalus. They remain cuboidal and heavily ciliated. Numerous microvilli cover the cell surface. The extracellular space of the neuropil is not expanded. Ependymal cells over the periventricular white matter are markedly modified. The characteristic response of these ependymal cells is to enlarge and to form lacunae in their apical cytoplasm. Their apical, horizontal cytoplasmic processes elongate as adjacent ependymal cells separate. The ex-tracellular space of the neuropil is expanded. It is proposed that the changes seen in ependymal cells over periventricular white matter are a response to enlargement of the ventricular surface permitted by the orientation of neuronal and glial fibers parallel to the ventricular surface. With expansion of the ventricular surface, overlapping apical processes become elongated and modified, containing a terminal web. With further enlargement, sliding of an overlapping apical process of one cell uncovers the apical process of its neighboring cell. By this mechanism, the ventricular surface area of any ependymal cell whose surface has been partially covered by its neighbor is increased. With further progression, this compensation fails and the neuropil is exposed to the ventricular cavity. Over caudate nucleus, expansion of ventricular surface is hindered by the disposition of fascie adherentes along intercellular clefts oriented perpendicular to the ventricular surface. Lateral sliding of horizontal apical processes does not occur as such processes are not found in ependyma over the caudate nucleus. The differential response of the ventricular surface in these two areas characteristically seen in hydrocephalus is; determined by regional differences in the morphology of their ependymal cells and underlying neuropil.  相似文献   
70.
A method of standardizing mitotic counts is described. This provisional approach, which expresses mitoses as a percentage of breast cancer cells present, holds the promise of facilitating interlaboratory agreement as well as providing a measure of tumor cellularity, probably an independent prognostic indicator in its own right. We suggest that this approach or one similar to it will maximize the evaluation and quantitation of proliferative activity from routinely available histologic material. Furthermore, the method is accomplished with little added effort beyond the customary histologic evaluation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号