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   201849篇
  免费   8005篇
  国内免费   406篇
耳鼻咽喉   3528篇
儿科学   7450篇
妇产科学   5348篇
基础医学   27982篇
口腔科学   5768篇
临床医学   15640篇
内科学   37114篇
皮肤病学   5248篇
神经病学   18666篇
特种医学   9867篇
外国民族医学   24篇
外科学   33309篇
综合类   1262篇
一般理论   51篇
预防医学   10222篇
眼科学   5235篇
药学   13826篇
中国医学   448篇
肿瘤学   9272篇
  2023年   1026篇
  2022年   858篇
  2021年   2022篇
  2020年   1602篇
  2019年   1975篇
  2018年   3805篇
  2017年   3154篇
  2016年   4112篇
  2015年   4421篇
  2014年   5047篇
  2013年   6995篇
  2012年   10427篇
  2011年   9998篇
  2010年   5859篇
  2009年   4729篇
  2008年   9332篇
  2007年   10339篇
  2006年   10235篇
  2005年   10721篇
  2004年   10086篇
  2003年   10011篇
  2002年   9864篇
  2001年   6908篇
  2000年   6984篇
  1999年   5978篇
  1998年   1801篇
  1997年   1472篇
  1996年   1141篇
  1995年   940篇
  1994年   878篇
  1992年   2665篇
  1991年   2544篇
  1990年   2467篇
  1989年   2334篇
  1988年   2009篇
  1987年   2028篇
  1986年   1880篇
  1985年   1792篇
  1984年   1371篇
  1983年   1106篇
  1979年   1487篇
  1978年   1085篇
  1977年   931篇
  1975年   1144篇
  1974年   1189篇
  1973年   1075篇
  1972年   1085篇
  1971年   1037篇
  1970年   925篇
  1969年   873篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We report a 24-year-old woman with an intramedullary conus ependymoma associated with holocord syringohydromyelia and syringobulbia. The tumor was removed and surgery for decompression of the syringohydromyelia was not considered at the first operation. In the follow-up examinations, MRI showed significant and steady improvement of syringohydromyelia. Symptoms associated with syringohydromyelia also disappeared. The cause of syringohydromyelia accompanying intradural spinal cord tumors appears to be either direct blockade of the central canal or secondary interruption of the central canal flow by compression of the perimedullary cerebrospinal fluid flow. As removal of the mass often corrects both these likely causes of the syringohydromyelia, no additional treatment for the drainage of the hydromyelia cavity syrinx is usually necessary.  相似文献   
72.
Fibrinopeptide A (FPA), platelet-secreted protein, platelet factor 4 and beta-thromboglobulin were determined in the cerebrospinal fluid of patients who had suffered from subarachnoid hemorrhage and were treated with 6 g tranexamic acid or 4 million KIU aprotinin to prevent rebleeding. Platelet-secreted proteins and FPA were cleared from the cerebrospinal fluid within 3 days after bleeding. Their vasoactive and thrombotic capability is limited to the initiation period of vasospasm that usually comes to clinical observation 3-8 days after bleeding. Increased thrombotic activity of the cerebrospinal fluid, as reflected by high levels of FPA and platelet-secreted protein, seemed to promote the occurrence of neurological deficits.  相似文献   
73.
The effects of acute stress exposure upon cholecystokinin (CCK) and substance P (SP) concentrations in discrete hypothalamic regions of the adult male rat brain were studied. Animals were exposed to foot shock stress for periods of 2, 4, 10, 30 or 60 min duration; immediately afterwards they were decapitated; brains were frozen and subsequently microdissected. CCK and SP concentrations were assayed by a specific RIA, as were serum levels of ACTH, corticosterone, PRL, GH, LH and testosterone. Stress had no effect upon SP concentrations in the anterior or posterior parts of the arcuate nucleus (ARC), but led to elevated CCK levels in the posterior ARC following 60 min of exposure. In both the ventromedial and dorsomedial hypothalamic areas, stress induced depletions of both neuropeptides. In the anterior (but not the posterior) portions of the lateral hypothalamic area, CCK and SP concentrations were reduced by stress exposure. These studies demonstrate that discrete hypothalamic CCK and SP neuronal systems are responsive to stress. This suggests that endogenous hypothalamic CCK and SP participate, along with other neurotransmitters/neuromodulators, in the integrated hypothalamic stress response, and mediate stress-neuroendocrine interactions.  相似文献   
74.
The objective of the present investigations was to develop oblong tablets which expand after contact with gastrointestinal fluids within a few minutes to a length of 4-6 cm and which should remain in the stomach for a prolonged period of time due to their size. The tablets were prepared from riboflavin-containing collagen sponges using a computer controlled single punch tablet machine. The collagen material was compressed to oblong tablets with dimensions of 3.5 mm x 9 mm x 18 mm. In vitro investigations were carried out to characterise drug release. The model drug riboflavin was released from the collagen tablets over 12h. The gastrointestinal retention time of the new dosage form was indirectly estimated by determining the duration of riboflavin excretion after oral intake of the tablet. A crossover in vivo study with 12 healthy male and female subjects was performed. The renal excretion of riboflavin was measured after oral administration of collagen tablets and small sustained release hydrocolloid tablets as reference preparation. The amount of riboflavin excreted into the urine was enhanced after administration of the expanding collagen tablets in comparison with the hydrocolloid tablets. The differences were statistically significant after 5, 6, 8, 9, 10 and 12 h.  相似文献   
75.
The effect of the divalent cations, Mn2+, Mg2+ and Ca2+ on rat forebrain delta-, mu- and kappa-receptor binding was examined during postnatal development. It was found that delta-receptor binding, assessed with [3H]D-Ala2-D-Leu5-enkephalin ([3H]DADLE) (+ 10 nM D-Ala2- MePhe4-Gly-ol5-enkephalin (DAMGE)), was stimulated by the 3 cations in a dose- and developmental time-dependent manner. delta-Binding was most sensitive to the cations during the first week postnatal, prior to the appearance of high-affinity delta-binding. In contrast, inhibition of mu-receptor binding ([3H]DAMGE) by divalent cations appeared early in development and remained constant throughout the postnatal period. Divalent cation inhibition of kappa-binding ([3H]ethylketocyclazocine ([3H]EKC) + 100 nM DAMGE and 100 nM DADLE) appeared after the second week postnatal. These results demonstrate that the characteristics and postnatal development of divalent cation modulation of mu-, delta- and kappa-binding is distinctly different. Thus, the neonate may be a good model system to examine the binding properties and functions of delta- and kappa-receptor subtypes.  相似文献   
76.
Background: Retinal pigment epithelium (RPE)lesions are predictive congenital phenotypic markersfor familial adenomatous polyposis (FAP). Thisprospective screening study aims at assessing theincidence and significance of these lesions in FAPpatients and their family members.Methods: Sixty-two members from three familiesincluding five patients with the diagnosis of FAP havebeen ophthalmologically surveyed. All RPE lesions weredocumented with fundus photography and fluoresceinangiography was performed in 13 subjects.Sigmoidoscopy and/or radiological examination wereperformed annually in 9 family members with typicalRPE lesions during 4 years to allow early diagnosis ofFAP.Results: Typical RPE lesions were present infive FAP patients and 15 family members.Telangiectatic dilatations in the retinal peripherywith small dot-like hemorrhages were detected in 6subjects from 3 families These lesions wereparticularly evident on fluorescein angiography.Annual colon analysis showed polyps in 3 out of 9subjects who were positive for RPE lesions.Conclusion: RPE lesions are valuable as aclinical marker in predicting FAP. The co-existingperipheral vascular alterations which have not beenreported before, are probably related to FAP.  相似文献   
77.
The present study investigated the expression of c-erbB-2 in 59 meningiomas, including different histological subtypes and anaplastic variants, by immunocytochemistry and molecular biological techniques. Immunohistochemistry using the monoclonal antibody FWP-51 directed against c-erbB-2-encoded oncoprotein gp185 demonstrated variable degrees of immunoreactivity in all meningiomas. The intensity of immunostaining correlated with the degree of expression as assessed by Western analysis in 28 meningiomas using polyclonal antiserum 21N. There was no correlation between the degree of expression and histological variants. Immunoreactivity of all menigiomas was distinctly less intense, however, than that of the human breast cancer cell line SK-BR-3, and slightly lower than that of brain metastases of breast and ovarian carcinomas that served as positive controls for both methods. By Southern analysis all meningiomas showed a single copy of the c-erbB-2 gene. Non-neoplastic arachnoid cap cells also exhibited c-erbB-2 expression and the degree of immunoreactivity was comparable with the majority of meningiomas. These data argue against an overexpression of c-erbB-2 in meningiomas, but rather indicate a cell-type-specific constitutive expression of the c-erbB-2 gene product in meningiomas and their putative progenitor cells. Since a subgroup of meningiomas is known to express progesterone receptors (PR), gp185 immunoreactivity was compared to the hormone receptor status using monoclonal antibody KD68. Fifty-six percent meningiomas showed PR immunoreactivity, but there was no statistically significant correlation with the degree of gp185 expression.This study was supported by a grant of the Tumorzentrum Heidelberg/Mannheim (M.K., No. 10028060)  相似文献   
78.
Bilateral germ cell tumours of the testis are rare but a rise in their incidence is expected since with the new therapeutic possibilities a significant improvement in prognosis has been achieved even in patients with advanced metastatic spread. Of the 210 patients treated for malignent germ cell tumours at our Department, six (2.9%) developed a contralateral testicular tumour. All patients had metachronous tumours and the second tumours occurred after an interval ranging between 1 and 22 years. The epidemiology, histology, diagnosis, therapy and prognosis are discussed, and the significance of regular self-examination of the remaining testis in patients with testicular tumour is emphasized.  相似文献   
79.
Summary Physeal distraction was applied with an external fixator to the triradiate cartilage of dogs with the aim of increasing the capacity of the acetabulum. The force was continued for from 2 to 6 weeks and the consequent changes were evaluated with regard to function and structure by radiography and microscopy. The distraction, without producing epiphysiolysis and destruction of the cartilage, resulted in expansion of the pelvic bones. The depth and volume of the acetabulum were increased, but the acetabular angle was decreased. Distraction also caused proliferation of the lacunar cells and the number of mammillary processes in the cartilage columns increased. Distraction can therefore be applied to the triradiate cartilage to enlarge the capacity of the acetabulum without producing epiphysiolysis.
Résumé Dans cette étude une distraction a été appliquée sur le cartilage en Y. Douze chiens bâtards, âgés de 2.5 à 4 mois, ont été utilisés pour cette expérimentation. Une force de distraction de 80 Newton a été appliquée d'emblée sur le cartilage en Y. L'application de cette force a été poursuivie sur les animaux pendant 2, 4 ou 6 semaines. A la fin de cette période, les changements de la cavité cotyloïde et du cartilage en Y ont été évalués sur le plan fonctionnel, morphologique, radiologique et histopathologique Aucune altération fonctionnelle n'a été mise en évidence dans les groupes opérés par rapport au groupe de contrôle. On a observé que la distraction a déterminé une expansion massive de l'ilion, du pubis et de l'ischion. Sur les hanches de contrôle la profondeur de la cavité cotyloïde a été évaluée à 13.5 mm, le volume à 1.96 cc et l'angle de la cavité cotyloïde à 29.9°. Après distraction ces valeurs ont été respectivement de 14.4 mm, de 2.10 cc et de 25.7°. La distraction entraîne donc un accroissement de profondeur et de volume de la cavité cotyloïde, mais inversement une diminution de l'angle de cette cavité. Ces résultats montrent que la distraction détermine une prolifération des cellules lacunaires et un accroissement des processus mammaires dans les colonnes du cartilage en Y. Ils montrent également qu'elle peut augmenter la taille de l'acetabulum.
  相似文献   
80.
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