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   1074572篇
  免费   73308篇
  国内免费   1365篇
耳鼻咽喉   15028篇
儿科学   34622篇
妇产科学   28687篇
基础医学   153504篇
口腔科学   29577篇
临床医学   95039篇
内科学   203798篇
皮肤病学   24422篇
神经病学   81514篇
特种医学   43085篇
外国民族医学   201篇
外科学   163255篇
综合类   21752篇
现状与发展   1篇
一般理论   263篇
预防医学   74709篇
眼科学   24544篇
药学   86235篇
  7篇
中国医学   2805篇
肿瘤学   66197篇
  2019年   7779篇
  2018年   11321篇
  2017年   8926篇
  2016年   10122篇
  2015年   11289篇
  2014年   15305篇
  2013年   22258篇
  2012年   30626篇
  2011年   32369篇
  2010年   19000篇
  2009年   17856篇
  2008年   30014篇
  2007年   32136篇
  2006年   32774篇
  2005年   31080篇
  2004年   29778篇
  2003年   28599篇
  2002年   27572篇
  2001年   60053篇
  2000年   61518篇
  1999年   50962篇
  1998年   12468篇
  1997年   11009篇
  1996年   11029篇
  1995年   10330篇
  1994年   9352篇
  1993年   8866篇
  1992年   37803篇
  1991年   36288篇
  1990年   35761篇
  1989年   34299篇
  1988年   30872篇
  1987年   30004篇
  1986年   28234篇
  1985年   26462篇
  1984年   19194篇
  1983年   16119篇
  1982年   8826篇
  1979年   17036篇
  1978年   11407篇
  1977年   10233篇
  1976年   8841篇
  1975年   10074篇
  1974年   11658篇
  1973年   11283篇
  1972年   10758篇
  1971年   10097篇
  1970年   9255篇
  1969年   8939篇
  1968年   7917篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
The return of fertility following discontinuation of norethisterone oenanthate (NET EN) 200 mg injectable contraceptive after use for a minimum period of six months or more was studied in 69 women who discontinued the method for planning pregnancy. Former users of copper intra-uterine device (CuT 200) were enrolled as a control group. Another 161 women who had discontinued NET EN due to other reasons (e.g. amenorrhoea, excessive bleeding or personal reasons) were also studied for return of fertility after ensuring that they were not using any other method of contraception and were exposed to the risk of pregnancy. The subjects from both groups were followed for a period of one year. The cumulative conception rates at one year were 72.5 and 83.6 per 100 subjects for ex-NET EN and ex-CuT 200 users who had discontinued the method for planning pregnancy and this difference was not statistically significant (P > 0.05). The median time for conception for ex-NET EN users was 7.8 months as compared to 3.7 months in ex-CuT 200 users but the cumulative conception rates at the end of one year show that future return of fertility in NET EN users does not appear to be adversely affected.

In 51 subjects who had discontinued NET EN due to amenorrhoea, the return of fertility was predictably slower and less. The return of fertility in subjects who discontinued NET EN for other reasons (e.g. excessive bleeding and other personal reasons) was similar to ex-NET EN and ex-CuT 200 users.  相似文献   

992.
Growing rats were fed ad libitum soy protein isolate (SPI) or its peptic (SPI-P) or tryptic digest (SPI-T) for a month and their sera were examined for cholesterol and triglyceride levels and enzyme activities such as cholinesterase, glutamate-pyruvate transaminase (GPT) and alkaline phosphatase. The rats fed SPI-P or SPI-T were inferior in growth to those fed SPI. Similarly, the serum glyceride level was lower in the SPI-P and SPI-T groups than in the SPI group. On the other hand, a significant difference was found in the serum cholesterol level between the SPI-P and SPI or SPI-T groups but not between the SPI and SPI-T groups. A similar tendency was observed for serum GPT and alkaline phosphatase activities, although there were no significant differences among dietary groups in small intestinal enzyme activities. As for the atherogenic index being a risk factor inducing atherosclerosis, the order of its value was SPI-P less than SPI less than SPI-T.  相似文献   
993.
Follicular fluids from eight patients with one ovary and from ten patients with two ovaries were investigated for bioactive inhibin, total renin, oestradiol (E2) and progesterone (P4) concentrations. Four follicular fluids were pooled per patient before assessment. All women had been stimulated similarly using a protocol including a GnRH agonist, HMG and HCG. Renin levels were significantly lower and P4 significantly higher in pools of follicular fluid from patients with one ovary, whereas inhibin and E2 concentrations were similar in both patient groups. A significant negative correlation was found in the pools of follicular fluid between inhibin and E2 in both groups. These results suggest a role for inhibin and renin in the paracrine and autocrine control of stimulated follicular development.  相似文献   
994.
The cytoskeleton is susceptible to oxidative stress and this occurs prior to membrane blebbing and cell lysis. Vimentin intermediary filaments in rheumatoid synoviocytes are more susceptible than in normal synoviocytes and this may have pathological significance. They are however no more susceptible to heat shock than other cell types.  相似文献   
995.
996.
Two distinct regions required for both contact hemolysis and entry into LLC-MK2 cells were cloned into Escherichia coli from the Shigella sonnei form I plasmid, pSS120. The first region was cloned into an E. coli HB101 strain containing noninvasive Tn1 insertion mutants of the form I plasmid, and expression of ipa (invasion plasmid antigen) gene products was restored. The plasmid carrying the first region was then transformed into E. coli lacking the form I plasmid, and additional DNA fragments from the form I plasmid were cloned into the same recipient on compatible vectors. Five of these double transformants were found to be positive for contact hemolysis activity. Restriction analysis of these five clones indicated that the previously reported ipa locus and the invA locus were present on the second plasmid region. Only the strains carrying both of these regions were active in contact hemolysis and cell invasion assays. Several proteins, including the a, b, c, and d proteins encoded by the ipa genes, were detected in the double transformants by Western blot (immunoblot) analysis with serum of a monkey convalescing from shigellosis. A positive regulator was suggested to exist in the first region, since the amounts of most of these proteins were simultaneously increased in the presence of this region. Subcloning and nucleotide sequencing indicated that this positive regulator gene was virF. Product analysis of the virF gene with minicells showed that two peptides (30 and 21 kilodaltons) were synthesized and that at least the 30-kilodalton protein was essential for regulation of the ipa genes.  相似文献   
997.
Solubilization of live Trichomonas vaginalis organisms with detergent caused the release of cysteine proteinases in the detergent extract which were inhibitable with N-alpha-p-tosyl-L-lysine chloromethyl ketone. The detergent extracts of all isolates tested possessed similar cysteine proteinase activities. These parasite proteinases rapidly degraded a prominent immunogen whose surface disposition undergoes phenotypic variation in some isolates. The relatedness of the forms of this immunogen among all isolates tested was confirmed by identical immunoblot patterns of autolysed immunogen, and data suggest the presence of repeating units or at least equidistant sites for proteinase cleavage within the immunogen molecule.  相似文献   
998.
Atrial natriuretic peptide (ANP) is a hormone release into the circulation by atrial cardiocytes (Gutkowska et al. 1984). Extracellular fluid volume expansion acts as a powerful stimulus for ANP secretion and results in the augmentation of its plasma concentration (Lang et al. 1985). Patients with active acromegaly demonstrate the increased extracellular fluid volume (Falkheden et al. 1964), while a successful treatment of the disease results in the disappearance of hypervolemia (Strauch et al. 1977). We have recently demonstrated that in patients with active acromegaly the increased total body plasma volumes are accompanied by the elevated plasma ANP concentrations, whereas, in the successfully treated patients, both: total plasma volumes and plasma ANP levels do not differ significantly from these in healthy subjects (Czekalski et al. 1988b).  相似文献   
999.
The effects of SCH 23390 (D1 dopamine receptor antagonist), SK&F 38393 (D1 dopamine receptor agonist), raclopride and remoxipride (D2 dopamine receptor antagonists) and ketanserin (5-hydroxytryptamine 2 receptor antagonist) on TSH serum levels (radioimmunoassay) and on brain catecholamine levels (Falck-Hillarp methodology in combination with quantitative histofluorimetry) were studied. SCH 23390 produced a dose-dependent increase in serum TSH levels in the lower dose range (0.01-0.03 mg kg-1, i.p.) administered 30 min before decapitation and in the higher dose range (1.0-3.0 mg kg-1) when given 2 h before decapitation. Following 30 min of treatment with the high doses of SCH 23390, reductions in serum TSH levels were found. The changes observed following SCH 23390 treatment occurred without affecting catecholamine levels in the median eminence and the peri- and paraventricular hypothalamic regions. Raclopride (0.1-10 mg kg-1, i.p.), remoxipride (1.0 mg kg-1, i.p.) or ketanserin (0.3 mg kg-1, i.p.) changed neither serum TSH levels nor brain catecholamine levels, SK&F 38393 (1.0-10 mg kg-1, i.p.) produced an increase in serum TSH levels. The results suggest the existence of inhibitory and facilitatory mechanisms regulating TSH secretion mediated via D1 dopamine receptors.  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