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   14109篇
  免费   706篇
  国内免费   93篇
耳鼻咽喉   154篇
儿科学   259篇
妇产科学   74篇
基础医学   1518篇
口腔科学   469篇
临床医学   912篇
内科学   3618篇
皮肤病学   403篇
神经病学   896篇
特种医学   554篇
外科学   2332篇
综合类   52篇
预防医学   436篇
眼科学   383篇
药学   1345篇
中国医学   18篇
肿瘤学   1485篇
  2023年   92篇
  2022年   195篇
  2021年   326篇
  2020年   193篇
  2019年   251篇
  2018年   343篇
  2017年   254篇
  2016年   295篇
  2015年   295篇
  2014年   382篇
  2013年   492篇
  2012年   773篇
  2011年   839篇
  2010年   514篇
  2009年   407篇
  2008年   738篇
  2007年   792篇
  2006年   807篇
  2005年   776篇
  2004年   711篇
  2003年   685篇
  2002年   697篇
  2001年   334篇
  2000年   379篇
  1999年   349篇
  1998年   148篇
  1997年   128篇
  1996年   124篇
  1995年   102篇
  1994年   84篇
  1993年   79篇
  1992年   211篇
  1991年   178篇
  1990年   181篇
  1989年   191篇
  1988年   171篇
  1987年   161篇
  1986年   136篇
  1985年   148篇
  1984年   120篇
  1983年   85篇
  1982年   44篇
  1981年   53篇
  1979年   65篇
  1978年   46篇
  1977年   45篇
  1973年   51篇
  1971年   42篇
  1969年   50篇
  1968年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A clone of NIH3T3 transformant (H3) can yield subcutaneous tumors and experimental pulmonary metastasis in nude mice. Compared to H3 in culture, the cells after in vivo tumor growth (H3-N) acquired enhanced tumorigenicity and metastatic ability. Also, indirect immunofluorescence revealed that cellular fibronectin (c-FN) of H3-N was decreased remarkably. We have studied the interactions between H3 and extracellular matrices to elucidate these phenomena. In the present study, we observed the effect of NIH3T3, H3, and H3-N cultured in type I collagen gel. Morphologically in the collagen gel, NIH3T3 assumed an extensive elongated fiber-like shape, H3 assumed a moderately elongated shape, and H3-N assumed a round or spindle shape with short pseudopodia. Compared to conventional cultures on dishes, cell proliferation of all three types was suppressed in collagen gel, but the degree of the suppression was least in H3-N. As a result, H3-N grew fastest in collagen gel. The variants which acquired growth advantage in the subcutaneum of mice also kept it in collagen gel. H3 cells were cultured in type I collagen gel for 4 weeks, a period comparable to that of tumor formation in nude mice. The cells after this long-term culture (H3-C) acquired enhanced tumorigenicity and metastatic ability nearly equal to that of H3-N. FACS analysis revealed that the c-FN of H3-C had decreased to a value comparable to that of H3-N. This means that type I collagen gel as well as subcutaneous tissues could select variants of H3 with less c-FN through proliferation. Moreover, it is suspected that lattices of type I collagen regulate cell proliferation of fibroblast via c-FN. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
62.
The 6-amino-6-deoxy-N-acetylmuramyldipeptides and their 6-acylamino derivatives were shown to be active as adjuvants on the induction of delayed-type hypersensitivity to azobenzenearsonate-N-acetyl-l-tyrosine in guinea pigs. However, 6-acylamino-6-deoxy-N-(acyl)muramyldipeptides were inactive as adjuvants.  相似文献   
63.
In the present study, small volumes of plasma were used for the measurement of bromvalerylurea (BVU), its metabolite, 3-methylbutyrylurea (MVU), and bromide in carbon tetrachloride (CCl4)-treated rats by HPLC-UV and energy dispersive X-ray spectrometry. A liquid-liquid extraction system was also investigated. BVU and MVU were extracted from 100 microl plasma samples in a single-step involving deproteination with 1 M hydrochloric acid using ethenzamide as internal standard. Samples were separated by HPLC in an acetonitrile-8 mM potassium dihydrogenphosphate buffer (35:65, v/v) mobile phase at a flow-rate of 0.4 ml/min on a 15 cm octadecylsilyl column at room temperature. Analytes were detected at a wavelength of 210 nm. The limits of quantitation for BVU, MVU and bromide are 0.1, 0.1 and 50 microg/ml, respectively. The intra-day accuracies over the range of concentrations were 95.8 to 121.1%, 97.2 to 119.7% and 96.2 to 105.8% for BVU, MVU and bromide, respectively. The inter-day accuracies were 97.7 to 115.1%, 98.3 to 111.6% and 98.3 to 102.9% for BVU, MVU and bromide, respectively. The absolute recoveries using tert.-butyl methyl ether are 96-98% for BVU and 95-98% for MVU. The decline in the plasma concentrations of BVU in olive oil-treated rats fitted a one-compartment model and the plasma MVU level reached a peak at around 1.5-2 h and then decreased gradually. The elimination of BVU in CCl4 (1 ml/kg)-treated rats was delayed and MVU production was less than that in the olive oil-treated group. However, there was no difference in the plasma levels of bromide between CCl4-treated rats and control rats. rights reserved.  相似文献   
64.
OBJECTIVES: We investigated the relationship between P16-immunostaining patterns and clinicopathological factors in early uterine cervix cancers and assessed whether P16-immunostaining patterns predict the prognosis of the patients with early uterine cervix cancers. METHODS: Twenty-nine early squamous cell carcinoma (SCC) specimens of the uterus were examined using immunohistochemistry for P16 expression. The P16-immunostaining pattern was classified into two groups: the homogeneous type and the heterogeneous type. P16-immunostaining patterns were evaluated in different parts of the carcinoma in situ (CIS): the center of the tumor and the front interface of the infiltrating tumor. RESULTS: All specimens were of the homogeneous type in CIS. The P16-immunostaining pattern was significantly of the heterogeneous type in the front interface of the infiltrating tumor with lymphatic invasion, vascular invasion, lymph node metastasis, and recurrence. Regarding the P16-immunostaining patterns in the front interface of the infiltrating tumor, the patients with the heterogeneous type showed a significantly worse prognosis than the patients with the homogeneous type. CONCLUSIONS: The prognosis of patients with early uterine cervical SCC may be predicted by evaluating the P16-immunostaining pattern in the front interface of the infiltrating tumor.  相似文献   
65.
66.
In this study, we developed a ratings scale for estimating sleep onset that would be capable of providing quantitative evaluations of the quality of the sleep onset process. We also examined factors affecting sleep onset using a questionnaire consisting of two separate clusters of items: the first, consisting of 9 items, related to the quality of sleep onset; and the second, consisting of 56 items, related to factors with apparent effects on sleep onset. The questionnaire was administered to 515 day-workers (range: 25-44 years old) for standardization. Each item was weighted based on the distribution of subject responses to determine discrimination. The reliability coefficient alpha for the questionnaire was high, exceeding 0.8. Of 41 items set out as potential factors affecting sleep onset, the results of the questionnaire indicated that five factors consisting of 26 items could be isolated as most likely affecting sleep onset. Path analysis indicated that sleep onset is more commonly affected by factors present at bedtime than factors related to sleep quality the previous night, or to daytime activities.  相似文献   
67.
Catastrophic antiphospholipid syndrome: CAPS]   总被引:1,自引:0,他引:1  
Antiphospholipid syndrome (APS) is well known as an autoimmune thrombotic syndrome with recurrent thromboses. In APS, thromboses occurs both artery and vein, and from large to micro vessels. In contrast, so called catastrophic antiphospholipid syndrome, CAPS, develops multiple thromboses at microvessels mainly within a few weeks and induces to poor prognosis. CAPS often occurs in patients with SLE or primary APS after a change of antithrombotic therapy, infection, and operation. Treatments for CAPS have not established although plasma exchange is carried out usually as well as intensive anticoagulation and immunosuppressive therapy. We treated with immunoadsorption plasmapheresis (IAPP) for 5 CAPS patients and they improved their clinical symptoms and ameliorated their titers of antiphospholipid antibodies. IAPP could be an useful treatment skill for CAPS and we have started prospective study.  相似文献   
68.
The effect of physical training on the cutaneous vascular response during transient exercise load is unclear. We determined the phase response and amplitude response of cutaneous vascular conductance (CVC) in the hand during sinusoidal exercise in endurance exercise-trained and untrained subjects. Subjects exercised on a cycle ergometer with a sinusoidal load for 32 min. The load variation ranged from 10% [23 (1) W in the trained group, 19 (1) W in the untrained group] to 60% [137 (4) W, 114 (6) W] of peak O2 uptake, and five different time periods (1, 2, 4, 8, and 16 min) were selected. Skin blood flow in the dorsal hand and palm were monitored by laser-Doppler flowmetry. CVC was evaluated from the ratio of blood flow to mean arterial pressure. During sinusoidal exercise, the amplitude of CVC was smaller in the dorsal hand than palm for shorter periods (1, 2, and 4 min) (P<0.05). The phase lag of CVC was smaller in the dorsal hand than palm for longer periods (8 and 16 min) (P<0.05). The amplitude response did not differ significantly between the two groups. The phase lag of CVC in the dorsal hand (P<0.05) and palm (P=0.06) was larger in the trained group than untrained group. These findings suggest that glabrous and nonglabrous skin vascular responses in the hand differ during transient exercise load, and physically trained subjects show a slower vascular response in the two skin areas to exercise stimulation than do untrained subjects.  相似文献   
69.
The marginal zone macrophages of the spleen are implicated in the clearance of polysaccharides, but underlying mechanisms need to be pinpointed. SIGN-R1 is one of five recently identified mouse genes that are homologous to human DC-SIGN and encode a single, external, C-terminal C-type lectin domain. We find that a polyclonal antibody to a specific SIGN-R1 peptide reacts primarily and strongly with a subset of macrophages in the marginal zone of spleen and lymph node medulla. In both sites, SIGN-R1 exists primarily in an aggregated form, resistant to dissociation into monomers upon boiling in SDS under reducing conditions. Upon transfection into three different cell lines, high-mol.-wt forms bearing SIGN-R1 are expressed, as well as reactivity with ER-TR9, a mAb previously described to react selectively with marginal zone macrophages. SIGN-R1-expressing macrophages preferentially sequester dextrans following i.v. injection. Likewise, when phagocytic cells are enriched from spleen and tested in culture, dextran is selectively endocytosed by a subset of very large SIGN-R1(+) cells representing approximately 5% of total released macrophages. Uptake of FITC-dextran by these macrophages in vivo and in vitro is blocked by ER-TR9 and polyclonal anti-SIGN-R1 antibodies. Following transfection with SIGN-R1, cell lines become competent to endocytose dextrans. The dextran localizes primarily to compartments lacking transferrin receptor and the LAMP-1 CD107a panlysosomal antigen. Therefore, SIGN-R1 mediates the uptake of dextran polysaccharides, and it is predominantly expressed in the macrophages of the splenic marginal zone and lymph node medulla.  相似文献   
70.
Mice deficient in the B cell adaptor for phosphoinositide 3-kinase (BCAP) have reduced numbers of mature B lymphocytes, which show defects in cell survival and proliferation. We found here that the NF-kappa B (Rel) pathway was impaired in BCAP-deficient mature B cells and that NF-kappa B target genes, indispensable for cell survival and division, were not induced in response to B cell receptor (BCR) stimulation. Among the NF-kappa B (Rel) family, expression of c-Rel was specifically reduced in BCAP-deficient B cells. Retrovirus-mediated reintroduction of c-Rel restored the pool size of immunoglobulin (Ig)M(lo)IgD(hi) mature B cells in the spleen as well as proliferative responses to BCR stimulation. These results indicate BCAP is essential in the maintenance of mature B cells through functional coupling with c-Rel.  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