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   4632篇
  免费   357篇
  国内免费   5篇
耳鼻咽喉   26篇
儿科学   180篇
妇产科学   91篇
基础医学   604篇
口腔科学   100篇
临床医学   518篇
内科学   1098篇
皮肤病学   51篇
神经病学   321篇
特种医学   252篇
外科学   619篇
综合类   69篇
一般理论   3篇
预防医学   431篇
眼科学   53篇
药学   333篇
中国医学   5篇
肿瘤学   240篇
  2023年   29篇
  2022年   22篇
  2021年   71篇
  2020年   41篇
  2019年   78篇
  2018年   78篇
  2017年   71篇
  2016年   77篇
  2015年   74篇
  2014年   94篇
  2013年   191篇
  2012年   265篇
  2011年   266篇
  2010年   165篇
  2009年   160篇
  2008年   256篇
  2007年   279篇
  2006年   274篇
  2005年   273篇
  2004年   209篇
  2003年   205篇
  2002年   207篇
  2001年   133篇
  2000年   132篇
  1999年   103篇
  1998年   47篇
  1997年   47篇
  1996年   56篇
  1995年   32篇
  1994年   35篇
  1993年   49篇
  1992年   73篇
  1991年   71篇
  1990年   93篇
  1989年   62篇
  1988年   54篇
  1987年   54篇
  1986年   46篇
  1985年   48篇
  1984年   30篇
  1983年   23篇
  1982年   22篇
  1981年   24篇
  1980年   24篇
  1979年   38篇
  1977年   22篇
  1975年   24篇
  1974年   32篇
  1973年   22篇
  1970年   23篇
排序方式: 共有4994条查询结果,搜索用时 553 毫秒
41.
42.
Y chromosome variation has been studied in three groups of Norwegian males: 35 boys from an adolescent psychiatric hospital; 45 men from a hospital for hard-to-manage or dangerous, psychotic men; and 26 boys from two ordinary school classes.
Y chromosomes with 1, 2, and 3 brightly fluorescing bands were found in all three groups. One boy carried a Y with no bands. The mean values of the Yf/Yq ratio were not significantly different in the three groups (Yf is the length of the distal, brightly fluorescing part of Yq). Two cases of XY/XYY mosaicism were found among the psychotic men.
The study shows that the human species is polymorphic with regard to the size of the Y chromosome, i. e. the number of fluorescent bands in the long arm. No phenotypical manifestation of this polymorphism, particuIarly as regards behaviour, was found.  相似文献   
43.
Part of the natural history of follicle center lymphoma (FCL) is transformation to a more aggressive neoplasm, almost always a diffuse large B-cell lymphoma. We describe a rare example of a precursor B-lymphoblastic transformation of grade I FCL occurring in a 45-year-old woman 12 years after initial presentation and 3 years after successful treatment for a diffuse large cell transformation. The lymphoblastic lymphoma shared the same immunoglobulin heavy chain gene rearrangement as the FCL as assessed by polymerase chain reaction amplification and direct sequencing, as well as identical kappa light chain gene rearrangements by Southern blot analysis. The immunoglobulin heavy chain variable gene sequences of both tumors showed numerous identical base substitutions compared with germline sequences and 3 additional mutations in the lymphoblastic lymphoma not present in the low-grade FCL. These results indicate origin of the lymphoblastic process from the mature follicle center B-cell clone, rather than divergent origin of the 2 tumors from a common immature B-cell precursor.  相似文献   
44.
The lengths of the index finger (2D) and ring finger (4D) are sexually dimorphic in humans, and men have a smaller 2D:4D ratio compared to women. Prenatal androgens appear to be important in the development of the 2D:4D sex difference, since it has been reported in children as young as 2 years old, and since humans exposed to supernormal prenatal androgen levels display a smaller 2D:4D ratio. We tested whether another mammalian species in which the process of peripheral sexual differentiation is androgen‐dependent might also show a sex difference in digit ratios. The 2D:4D ratio of adult outbred mice was calculated for both the left and right rear paws. A sex difference was observed in the right rear paw: female mice had a larger 2D:4D ratio than did males. We also found this difference in prepubescent weanling mice. This sex difference is in the same direction as that observed in humans, and suggests that sexual dimorphism in digit length ratios is a feature common to many, if not all, mammals. The mouse may therefore be a useful animal model for studying the factors that influence finger length patterns, which have recently been correlated with several specific behaviors and disease predispositions in humans. Anat Rec 267:231–234, 2002. © 2002 Wiley‐Liss, Inc.  相似文献   
45.
46.
The classification of CD5-negative/CD10-negative chronic B-cell leukemias (CD5-/CD10- CBL) can be problematic. Most of these cases may represent leukemic non-Hodgkin's lymphoma (NHL) other than B-cell chronic lymphocytic leukemia (BCLL); nonetheless, some investigators still advocate the term "CD5-negative BCLL." Because adhesion molecule (AdMol) expression patterns reflect the biology of lymphoid neoplasms, we studied a series of 106 B-cell lymphoproliferative disorders, including CD5+ BCLL (n = 56), NHL other than BCLL (n = 35), and CD5-/CD10- CBL (excluding hairy cell leukemia and prolymphocytic leukemia) with no prior history of NHL (n = 15) for expression of components of the very late antigen-4 complex (alpha4/beta1 integrin (CD49d/CD29)), components of the mucosal addressin-cell adhesion molecule receptor (alpha4(CD49d)/beta7 integrin), and L-selectin (CD62L). CD62L expression was significantly greater in CD5+ BCLL than in NHL (P < .001). Conversely, CD29, CD49d, and beta7-integrin expression were significantly greater in NHL than in CD5+ BCLL (P < .001 for each marker). These differences persisted when only blood and bone marrow samples were analyzed, with the exception of differences in CD62L expression, which approached, but did not reach, statistical significance (P = .08). The group of CD5-/CD10- CBL displayed an AdMol profile similar to NHL and was significantly different than CD5+ BCLL in expression of beta7 integrin, CD29, CD49d, and CD62L (P range < .001-.011). In summary, CD5-/CD10- CBL display an AdMol profile resembling NHL and significantly different from CD5+ BCLL, supporting the growing notion that "CD5-negative BCLL" generally represents leukemic NHL rather than a variant of true CD5+ BCLL.  相似文献   
47.
Recent advances in cellular immunology: implications for immunity to cancer   总被引:8,自引:0,他引:8  
Basic immunologists, animal experimenters and clinicians came together earlier this year to discuss insights into, and applications of, cellular immunity to cancer. Major questions critical to the further evaluation and exploitation of the cellular immune response to cancer were explored. It was clear from this conference that there has been a move beyond phenomenology to reductionistic approaches to understanding immune events, raising hopes that the specificity of the T-cell response might be applied to the problem of human cancer.  相似文献   
48.
The isotype distribution of human IgG antibodies reactive with common dietary proteins has been evaluated in sera from adult patients with the irritable bowel syndrome and with bronchial asthma using a solid-phase immunoassay (ELISA). In both these medical disorders, serum antibodies reactive with ovalbumin or gliadin were restricted predominantly to the IgG4 isotype; however, IgG antibodies reactive with bovine milk antigens, notably casein, were often restricted to both the IgG2 and IgG4 isotypes. A similar serum IgG antibody isotype distribution for these dietary protein antigens was also demonstrated in IgG antibody-positive healthy adults. These data amplify the view that production of antibodies of the IgG4 isotype may reflect a normal immune response to dietary protein antigens presented at mucosal surfaces.  相似文献   
49.
Antigen-coupled antigen-presenting cells (APC) serve as potent tolerogens for inhibiting immune responses in vivo and in vitro, apparently by providing an antigen-specific signal through the TCR in the absence of co-stimulation. Although this approach has been well studied in rodents, little is known about its effects on human T cells. We evaluated the specificity and mechanisms of tolerization of human T cells in vitro using monocyte-enriched adherent cells that were pulsed with antigen and treated with the cross-linker, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (ECDI). Autologous antigen-coupled APC selectively tolerized T cells of the T(h)1 but not T(h)2 lineage through a mechanism that involved both antigen-specific and antigen-non-specific elements. The tolerization process was dependent on the ECDI and antigen concentration, and the coupling time, and was reflected by initial up-regulation of CD25. However, upon re-stimulation with fresh APC and antigen, tolerized T(h)1 cells failed to proliferate or to produce T(h)1 cytokine message or secreted protein, had decreased expression of CD25, CD28 and B7 and increased expression of MHC class II molecules, and demonstrated an enhanced commitment to apoptosis. T(h)1 cell tolerization could be prevented by adding anti-CD28 antibody, IL-2 or untreated APC at the same time as the ECDI/antigen-coupled APC, or reversed by adding anti-CD28 antibody or IL-2 upon re-stimulation with fresh APC plus antigen. Thus, the tolerizing effect of ECDI/antigen-coupled APC on human T(h)1 cells appears to involve a reversible anergy mechanism leading to apoptosis, whereby the targeted T cells receive full or partial activation through the TCR, without coordinate co-stimulation. These data suggest dichotomous signaling requirements for inactivating cells of the T(h)1 and T(h)2 lineages that may have important implications for treatment of T(h)1-mediated autoimmune or inflammatory diseases.  相似文献   
50.
The use of the Arden gratings (AO contrast sensitivity system) in optometric practice is evaluated. A total of 320 patients presenting for eye examination were screened with the gratings. Sixty-four eyes (10%) gave abnormal grating scores although results from conventional examination techniques revealed no abnormality. Of the 110 abnormal eyes detected by routine examination techniques, 8 presented with normal grating scores, 6 with "borderline suspect" scores and 96 with abnormal scores. Used in isolation, the failure rate of the Arden gratings to detect ocular abnormality in the patient population was 1.3% and the "false positive" referral rate was 10%.  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