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   41594篇
  免费   2417篇
  国内免费   159篇
耳鼻咽喉   254篇
儿科学   1345篇
妇产科学   726篇
基础医学   3263篇
口腔科学   569篇
临床医学   2628篇
内科学   6177篇
皮肤病学   649篇
神经病学   1226篇
特种医学   1201篇
外科学   5218篇
综合类   9533篇
一般理论   9篇
预防医学   7736篇
眼科学   299篇
药学   1735篇
  41篇
中国医学   824篇
肿瘤学   737篇
  2024年   83篇
  2023年   515篇
  2022年   1004篇
  2021年   1345篇
  2020年   1116篇
  2019年   3142篇
  2018年   2737篇
  2017年   1581篇
  2016年   758篇
  2015年   817篇
  2014年   2340篇
  2013年   2028篇
  2012年   2223篇
  2011年   2299篇
  2010年   1909篇
  2009年   1637篇
  2008年   1494篇
  2007年   1310篇
  2006年   1218篇
  2005年   826篇
  2004年   617篇
  2003年   498篇
  2002年   345篇
  2001年   306篇
  2000年   270篇
  1999年   239篇
  1998年   183篇
  1997年   186篇
  1996年   130篇
  1995年   136篇
  1994年   113篇
  1993年   50篇
  1992年   23篇
  1991年   29篇
  1990年   23篇
  1989年   20篇
  1986年   18篇
  1985年   852篇
  1984年   1391篇
  1983年   1111篇
  1982年   1100篇
  1981年   1102篇
  1980年   955篇
  1979年   844篇
  1978年   660篇
  1977年   464篇
  1976年   632篇
  1975年   552篇
  1974年   469篇
  1973年   430篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Rat submandibular gland tissue pieces were stimulated in vitro for 30 min with a beta-adrenergic agent or a cyclic AMP analog to stimulate protein secretion, or with alpha-adrenergic or cholinergic agents or a Ca2+ ionophore to stimulate fluid secretion. Acinar cells were examined by transmission electron microscopy. In control tissue, acinar cells showed little evidence of secretory activity. The Golgi apparatus was sparse and was associated with a few small, immature secretory granules with fine fibrillar contents. Following secretory granule discharge stimulated by isoproterenol or dibutyryl cyclic AMP, acinar cells were constricted, and had extensive basolateral membrane folding and tightly packed rough endoplasmic reticulum. Golgi complexes were prominent and had multiple small granules with filamentous contents. After stimulation of fluid secretion by alpha-adrenergic agents (epinephrine, phenylephrine), or cholinergic agents (acetylcholine, carbachol, pilocarpine), or a Ca2+ ionophore (A23187), the Golgi apparatus had compact concave cisternae enclosing aggregates of tubulovesicles. Acinar cells were distended, basolateral membranes were expanded, and rough endoplasmic reticulum was dilated and vesiculated.  相似文献   
102.
The calcium ionophore A23187(A23) at concentrations exceeding 1 microgram/ml has been shown to be progressively cytotoxic for human blood basophils, neutrophils, lymphocytes, and erythrocytes. Toxicity to basophils was considered to be manifested by the increasing inability of 2-deoxyglucose (2DG) to inhibit histamine release (HR) at increasing concentrations of A23. The toxicity to neutrophils and lymphocytes was demonstrated by decreased lactate production (LP) after incubation with A23 of Ficoll-Hypaque fractions greatly enriched in each respective cell type. Red cells present in dextran-sedimented leukocytes were increasingly susceptible to lysis during washing subsequent to exposure to increasing concentrations of A23. A concentration of 4 microgram A23/ml, which is cytotoxic at 37 degrees C, produced optimal and noncytotoxic HR at 22 degrees C. It was possible to reduce A23 concentrations required for optimal HR by increasing Ca++ from 0.6 to 3 mM.  相似文献   
103.
Several recent reports have described cases of acute nonlymphocytic leukemia with a unique chromosome translocation, t(6;9)(p23;q34). We have studied three additional patients who have acute nonlymphocytic leukemia and t(6;9)(p23;q34). Our findings provide additional support for the suggestion that this translocation is yet another distinct cytogenetic abnormality associated with myeloproliferative disorders.  相似文献   
104.
We encountered a 38-year-old Japanese male patient with chronic myelogenous leukemia (CML), whose bone marrow and peripheral blood cells during the chronic and blastic phases contained a complex Ph1 translocation and an extra Y chromosome [i.e., 47,XYY,t(9;22;13)(q34;q11;q14)]. A karyotypic analysis of PHA-stimulated lymphocytes showed the constitutional karyotype to be 47,XYY. Thus, it was considered that CML with a complex Ph1 translocation developed in an XYY male; such a case has not been reported, so far. A B-lymphocyte cell line with the complex Ph1 translocation was established by the procedure of Epstein-Barr virus transformation. The presence of the complex Ph1 translocation in the B-lymphocyte cell line suggests that some of the B lymphocytes in this patient originated from the CML clone.  相似文献   
105.
106.
107.
Effect of prostaglandin D2 and I2 on the airways of rhesus monkeys   总被引:2,自引:0,他引:2  
Prostaglandin (PG) D2 and PGI2 were evaluated to determine their effect on pulmonary function parameters when aerosolized in anesthetized rhesus monkeys. PGD2 resulted in an increase in frequency (f) and pulmonary resistance (rl) and a decrease in peak expiratory flow rate (PEFR), tidal volume (VT), and dynamic compliance (Cdyn), with the major effect on RL. PGI2 primarily effected an increase in f and a decrease in PEFR and VT. PGI2 had a variable effect, generally a decrease, on RL. The metabolite of PGI2, 6-keto-PGF 1 alpha, had no effect on the rhesus airway. PGF 2 alpha responses were similar to PGD2 except that the PGF 2 alpha produced a less strikingly consistent increase in RL. When PGI2 and PGD2 were aerosolized simultaneously, they simulated previously described antigen responses. Further, PGI2 plus PGD2 produced an airway response at 1/10 the concentration of either agent alone.  相似文献   
108.
We have analyzed the structural proteins of the C-type viruses produced by cloned lines of the MOPC-21 and FLOPC-1 BALB/c murine myelomas. These viruses, designated MO21-MuMAV and FL1-MuMAV, respectively, have been shown to be composed of proteins with approximate molecular weights of 90,000, 75,000, 17,000, 12,000, and 10,000 daltons. In addition, these viruses contain a “doublet” with molecular weights of approximately 30,000 daltons. The 90,000- and 75,000-dalton proteins are glycosylated. The p30 “doublet” as well as the NB-ecotropism is retained upon subsequent virus cloning in SC-1 cells, passage through NIH-3T3, or BALB/3T3 cells, or microtiter plate cloning of SC-1 cells replicating cloned virus. The two cloned MuMAVs appeared to possess the p30 proteins of the endogenous BALB/c N- and B-tropic viruses described by Hopkins and co-workers (N. Hopkins, J. Schindler, and R. Hynes, 1977, J. Virol.21, 309–318; J. Schindler, R. Hynes, and N. Hopkins, 1977, J. Virol. 23, 700–707). Subsequent tryptic peptide analysis of the myeloma virus p30 proteins demonstrated that these proteins share extensive homology with, but not identity to, the two prototype BALB/c ecotropic endogenous virus p30 proteins.  相似文献   
109.
A recently reported device, the sorbent suspension reciprocating dialyser (SSRD), was investigated for use as a test system for biocompatibility of dialyser components. The device is easy to assemble and operate, and allows minimal blood contact with foreign material outside of dialyser components. Its constant pressure/ variable flow rate operation allows quantification of degree of clotting of dialyser versus time. The effect of heparinization of the blood distribution gaskets (BDG) of the device on performance and dialyser lifetime was investigated. Heparin was bound to the surface of polyethylene gaskets by immersion in a solution of tridodecylmethylammonium chloride (TDMAC)-heparin complex for several hours. Gaskets were then assembled in an SSRD which was then used for experimental dialysis in dogs with AV shunts. Dialysers assembled using non-heparinized gaskets were used as controls. Blood coagulation tendency was quantified by the activated clotting time (ACT) and partial thromboplastin time (PTT), and these values correlated with the rate of clotting of the device. Heparinization of the gaskets resulted in the prevention of clotting in the dialyser until the final minutes of dialysis in all cases, in contrast to the constant decay of blood fill volume and evidence of clotting in the non-heparinized cases. However, dialyser lifetime was not significantly increased by gasket heparinization. At normal initial values of ACT (80–95 s) dialyser clotting occurred in 10–15 mia In tests with non-heparinized gaskets and systemically heparinized dogs, values obtained in the ACT test were observed to decrease during dialysis, indicating the disappearance of heparin from the blood. Both ACT and PTT tests show promise as predictors of dialyser lifetime.  相似文献   
110.
We have studied 46 Hymenoptera-allergic patients and 11 nonallergic controls by grading the severity of their sting reaction, determining their skin test reactivity, and performing human leukocyte histamine release with a commercial mixed stinging insect extract. A significant correlation was found between increasing severity of sting reaction and increasing skin test reactivity (p < 0.001). In 4146 allergic patients from 15 to 100 per cent release of total cellular histamine occurred, whereas in the 11 nonallergic controls no greater than 10 per cent release of total cellular histamine was observed. Skin test reactivity correlated significantly with cell sensitivity in the allergic patients (p < 0.001). Following hyposensitization therapy, cell sensitivity generally did not change, but significant increases in antigen-neutralizing capacity (A.N.C.) of allergic serum did occur in 1115 Hymenoptera-allergic patients.  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