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   25213篇
  免费   2367篇
  国内免费   65篇
耳鼻咽喉   262篇
儿科学   564篇
妇产科学   352篇
基础医学   3107篇
口腔科学   795篇
临床医学   3281篇
内科学   5388篇
皮肤病学   611篇
神经病学   1889篇
特种医学   964篇
外科学   3552篇
综合类   457篇
一般理论   24篇
预防医学   2713篇
眼科学   353篇
药学   1986篇
中国医学   24篇
肿瘤学   1323篇
  2021年   372篇
  2020年   216篇
  2019年   357篇
  2018年   390篇
  2017年   283篇
  2016年   342篇
  2015年   387篇
  2014年   530篇
  2013年   849篇
  2012年   1161篇
  2011年   1151篇
  2010年   636篇
  2009年   581篇
  2008年   1056篇
  2007年   1066篇
  2006年   1098篇
  2005年   1118篇
  2004年   1037篇
  2003年   980篇
  2002年   981篇
  2001年   976篇
  2000年   1004篇
  1999年   844篇
  1998年   297篇
  1997年   252篇
  1996年   237篇
  1995年   251篇
  1994年   201篇
  1993年   206篇
  1992年   608篇
  1991年   629篇
  1990年   583篇
  1989年   515篇
  1988年   484篇
  1987年   478篇
  1986年   474篇
  1985年   470篇
  1984年   339篇
  1983年   293篇
  1982年   217篇
  1981年   205篇
  1979年   324篇
  1978年   238篇
  1977年   201篇
  1975年   165篇
  1974年   214篇
  1973年   204篇
  1972年   169篇
  1971年   192篇
  1970年   170篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Poor control of clinic and 24-h blood pressure (BP) is associated with enhanced risk of all cardiovascular disease events. Certain patient groups including the elderly, African-Americans, and those with hypertension and comorbid disease are difficult to control, as are patients with stage 2 hypertension (systolic BP>or=160 mmHg or diastolic BP>or=100 mmHg). It has been estimated that more than two-thirds of high-risk hypertensive patients with stage 2 hypertension and all hypertensive patients with diabetes mellitus or kidney disease will require two or more antihypertensive agents from different therapeutic classes to reach BP goals. Combining agents with distinct and complementary modes of action can address different pathophysiologic mechanisms involved in hypertension and may lead to more complete and prompt reductions in BP. Tolerability may also improve, as certain classes of antihypertensive agents ameliorate adverse effects associated with other agents. Patients may benefit from fixed-dose combinations of drugs as this simplifies the regimen and may improve adherence with therapy, control of BP, and ultimately lead to reductions in cardiovascular events. Recent data and treatment guidelines support the use of a combination strategy as 'initial' antihypertensive therapy in high-risk patients with stage 2 hypertension.  相似文献   
992.
993.
OBJECTIVES: This study sought to assess long-term outcome and determine its predictors among 30-day survivors of cardiogenic shock. BACKGROUND: Patients with cardiogenic shock have high in-hospital and 30-day mortality, but there are little data about those who survive beyond 30 days. METHODS: We analyzed baseline, in-hospital, and survival data from patients in the U.S. with ST-segment elevation myocardial infarction (STEMI) and cardiogenic shock enrolled in the GUSTO (Global Utilization of Streptokinase and Tissue-Type Plasminogen Activator for Occluded Coronary Arteries)-I trial and compared them with patients in the same trial who did not have shock. RESULTS: Of 22,883 patients enrolled in the U.S., shock occurred in 1,891 (8.3%); 953 (50.4%) survived 30 days and 527 (27.8%) survived 11 years. Of 20,992 U.S. patients without shock, 20,360 (96.9%) survived 30 days and 14,131 (67.3%) survived 11 years. After the first year, 2% to 4% of patients died each year regardless of whether they had cardiogenic shock. Using Cox proportional hazards models, we were able to predict long-term mortality in all U.S. GUSTO-I 30-day survivors from their baseline demographics and in-hospital complications. The strongest predictors were diabetes mellitus, cardiogenic shock, hypertension, previous myocardial infarction, current smoking, anterior infarct, higher Killip class, higher heart rate, and older age; patients >75 years were at highest risk. Percutaneous revascularization during the index hospitalization was associated with a reduced risk of death. CONCLUSIONS: Among patients with cardiogenic shock who survive 30 days after STEMI, annual mortality rates of 2% to 4% approximate those of patients without shock.  相似文献   
994.
995.
Schizosaccharomyces pombe cells that cannot synthesize spermidine or spermine because of a deletion-insertion in the gene coding for S-adenosylmethionine decarboxylase (Deltaspe2) have an absolute requirement for spermidine for growth. Flow cytometry studies show that in the absence of spermidine an overall delay of the cell cycle progression occurs with some accumulation of cells in the G(1) phase; as little as 10(-6) M spermidine is sufficient to maintain normal cell cycle distribution and normal growth. Morphologically some of the spermidine-deprived cells become spherical at an early stage with little evidence of cell division. On further incubation in the spermidine-deprived medium, growth occurs in most of the cells, not by cell division but rather by cell elongation, with an abnormal distribution of the actin cytoskeleton, DNA (4', 6-diamidino-2-phenylindole staining), and calcofluor-staining moieties. More prolonged incubation in the spermidine-deficient medium leads to profound morphological changes including nuclear degeneration.  相似文献   
996.
Escolar  G; Leistikow  E; White  JG 《Blood》1989,74(6):1983-1988
We have examined the movement of fibrinogen-gold (fgn-Au) complexes in platelets activated in suspension and by surface contact. Fgn-Au probes did not react with resting cells but were bound to the external membrane of platelets in suspension 5 seconds after addition of 1 U/mL of thrombin. At intervals over a period of 5 to 20 minutes, fgn-Au probes moved from the cell surface to peripheral and then deep channels of the open canalicular system (OCS). When platelets were surface activated by exposure to carbon-stabilized, formvar-coated grids for 5 to 20 minutes and then exposed to fgn-Au complexes for 5 minutes, probes were also observed in the OCS. At 5 minutes, over 40% of the platelets had concentrated fgn-Au in their OCS. Results after 10 minutes revealed 25% with gold-filled channels, 16% after 15 minutes, and 5% after 20 minutes. The decrease in frequency of OCS staining correlated with the increasing frequency of spread platelets, suggesting that tension produced by spreading may cause collapse of the OCS or that the OCS may evaginate onto the platelet during spreading. To evaluate the latter hypothesis, platelets were initially exposed to grids for 5 minutes and then incubated with fgn-Au for intervals of 5 to 20 minutes. The frequency of platelets with fgn-Au concentrated in the OCS was greatest at 5 minutes (44%) and decreased at the same rate as the frequency of spread platelets increased. Only 14.7% of the cells contained fgn-Au in the OCS after 20 minutes. These were primarily dendritic in form, while fully spread platelets rarely contained an OCS filled with the probe. The study indicates that fgn-Au particles are cleared to channels of the OCS independent of the mechanism of platelet activation. Fgn-Au that has been concentrated in the OCS at early stages of surface activation can be externalized during platelet spreading but remain internalized in suspension-activated cells. The OCS represents a membrane reservoir that can be evaginated onto the platelet surface during interaction with surfaces.  相似文献   
997.
The present study evaluates whether the associative interactions between synapses that lead to long-term potentiation and depression (LTP and LTD) can occur between spatially segregated synapses of the medial and lateral temporodentate pathway of the rat. Coconditioning of crossed and ipsilateral pathways resulted in LTP of the crossed system only when the current sinks of the two conditioned pathways overlapped sufficiently. Likewise, conditioning of an ipsilateral pathway alone resulted in LTD of the crossed pathway only when those current sinks overlapped sufficiently. These observations support the idea that associative events that lead to LTP or LTD can be restricted to a local dendritic domain. The postsynaptic cell can therefore serve as more than one unit of integration for synaptic modification.  相似文献   
998.
Cloning of cDNA encoding steroid 11 beta-hydroxylase (P450c11).   总被引:6,自引:3,他引:6       下载免费PDF全文
We have isolated bovine and human adrenal cDNA clones encoding the adrenal cytochrome P-450 specific for 11 beta-hydroxylation (P450c11). A bovine adrenal cDNA library constructed in the bacteriophage lambda vector gt10 was probed with a previously isolated cDNA clone corresponding to part of the 3' untranslated region of the 4.2-kilobase (kb) mRNA encoding P450c11. Several clones with 3.2-kb cDNA inserts were isolated. Sequence analysis showed that they overlapped the original probe by 300 base pairs (bp). Combined cDNA and RNA sequence data demonstrated a continuous open reading frame of 1509 bases. P450c11 is predicted to contain 479 amino acid residues in the mature protein in addition to a 24-residue amino-terminal mitochondrial signal sequence. A bovine clone was used to isolate a homologous clone with a 3.5-kb insert from a human adrenal cDNA library. A region of 1100 bp was 81% homologous to 769 bp of the coding sequence of the bovine cDNA except for a 400-bp segment presumed to be an unprocessed intron. Hybridization of the human cDNA to DNA from a panel of human-rodent somatic cell hybrid lines and in situ hybridization to metaphase spreads of human chromosomes localized the gene to the middle of the long arm of chromosome 8. These data should be useful in developing reagents for heterozygote detection and prenatal diagnosis of 11 beta-hydroxylase deficiency, the second most frequent cause of congenital adrenal hyperplasia.  相似文献   
999.

Background

This article examines the incidence of venous thromboembolism (VTE) in combat wounded, identifies risk factors for pulmonary embolism (PE), and compares the rate of PE in combat with previously reported civilian data.

Methods

A retrospective review was performed of all U.S. military combat casualties in Operation Enduring Freedom and Operation Iraqi Freedom with a VTE recorded in the Department of Defense Trauma Registry from September 2001 to July 2011. The Military Amputation Database of all U.S. military amputations during the same 10-y period was also reviewed. Demographic data, injury characteristics, and outcomes were evaluated.

Results

Among 26,634 subjects, 587 (2.2%) had a VTE. This number included 270 subjects (1.0%) with deep venous thrombosis (DVT), 223 (0.8%) with PE, and 94 (0.4%) with both DVT and PE. Lower extremity amputation was independently associated with PE (odds ratio [OR], 1.70; 95% confidence interval [CI], 1.07–2.69). A total of 1003 subjects suffered a lower extremity amputation, with 174 (17%) having a VTE. Of these, 75 subjects (7.5%) were having DVT, 70 (7.0%) were having PE, and 29 (2.9%) were found to have both a DVT and a PE. Risk factors found to be independently associated with VTE in amputees were multiple amputations (OR, 2; 95% CI, 1.35–3.42) and above the knee amputation (OR, 2.11; 95% CI, 1.3–3.32).

Conclusions

Combat wounded are at a high risk for thromboembolic complications with the highest risk associated with multiple or above the knee amputations.  相似文献   
1000.
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