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   4309篇
  免费   210篇
  国内免费   9篇
耳鼻咽喉   51篇
儿科学   446篇
妇产科学   84篇
基础医学   509篇
口腔科学   56篇
临床医学   249篇
内科学   830篇
皮肤病学   59篇
神经病学   182篇
特种医学   109篇
外科学   554篇
综合类   154篇
预防医学   299篇
眼科学   173篇
药学   524篇
中国医学   23篇
肿瘤学   226篇
  2022年   54篇
  2021年   76篇
  2020年   38篇
  2019年   55篇
  2018年   80篇
  2017年   53篇
  2016年   77篇
  2015年   95篇
  2014年   118篇
  2013年   163篇
  2012年   188篇
  2011年   209篇
  2010年   163篇
  2009年   128篇
  2008年   212篇
  2007年   206篇
  2006年   221篇
  2005年   192篇
  2004年   201篇
  2003年   175篇
  2002年   134篇
  2001年   117篇
  2000年   136篇
  1999年   119篇
  1998年   52篇
  1997年   38篇
  1996年   33篇
  1995年   23篇
  1994年   28篇
  1993年   40篇
  1992年   72篇
  1991年   69篇
  1990年   72篇
  1989年   76篇
  1988年   72篇
  1987年   60篇
  1986年   61篇
  1985年   66篇
  1984年   51篇
  1983年   44篇
  1980年   37篇
  1979年   38篇
  1978年   32篇
  1977年   31篇
  1975年   38篇
  1974年   38篇
  1973年   23篇
  1972年   25篇
  1971年   26篇
  1970年   31篇
排序方式: 共有4528条查询结果,搜索用时 15 毫秒
11.
The order of abundance of different mallophagan species on poultry birds in Dehradun (India) has been found to be Menopon gallinae greater than Menacanthus cornutus greater than Menacanthus stramineus greater than Goniocotes gallinae greater than Goniodes dissimilis greater than Lipeurus caponis greater than Lipeurus lawrensis tropicalis greater than Goniodes gigas. The intensity of these species upon 1249 birds has been recorded by coding system. The correlation between the monthly incidence of different species and environmental temperature as well as R.H. has been recorded. The degree of association between four most commonly occurring combinations has also been analysed.  相似文献   
12.
In vitro treatment of mouse lymphocytes with an intracellular calcium chelator BAPTA-AM significantly decreased lectin Concanavalin-A (Con-A)-induced and mixed lymphocyte reaction (MLR) mediated, alloantigen-induced lymphocyte activation as indicated by decreased percentage of lymphoblasts among the BAPTA-treated lymphocytes. In vivo treatment of mice with intracellular Ca(2+) antagonist TMB-8 was found to substantially impair delayed type hypersensitivity (DTH; cell mediated immune) response, as indicated by decreased footpad swelling on tuberculin challenge of mice sensitized with BCG, after a single treatment with a low dose of 0.01mg of TMB-8 per mouse. Interestingly, a second injection of a higher dose of TMB-8 (0.1mg per mouse) resulted in very significant (p=0.001) abrogation of DTH as indicated by complete absence of swelling of foot pad after PPD challenge in BCG-primed treated mice. All mice in this group showed fully impaired DTH response. Lymphocytes of allosensitized mice gave a significantly higher (p<0.05) MLR response than the na?ve mice. However, a single treatment of allosensitized mice with 0.1mg TMB-8 resulted into a lower MLR response, comparable in magnitude to that of untreated na?ve mice.  相似文献   
13.
Using whole-cell patch-clamp techniques we found that ATP activated an outwardly rectifying current in Daudi human B lymphoma cells under acidic conditions. The substitution of Cl for gluconate shifted the reversal potential, while Cl channel blockers, 4,4-diisothiocyanostibene-2,2-disulfonic acid (DIDS) and 9-anthracene carboxylic acid (9-AC), blocked the current, indicating that ATP induces this current by activating the outwardly rectifying chloride channel (ORCC). The effect of ATP on ORCC was mimicked by ADP, but not by other P2 receptor agonists such as ATPS (a poorly hydrolyzable analog of ATP), 2,3-O-benzoyl-4-benzoyl-ATP (BzATP), and UTP. The ATP-induced ORCC current was completely blocked by 100 M suramin (a P2 receptor antagonist), and was partially blocked by 100 M pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid tetrasodium (PPADS), which is another P2 receptor antagonist. Neither inactivation of G proteins nor elimination of extracellular Ca2+ affected the ATP-induced current, indicating that G protein-coupled P2Y receptors and Ca2+-permeable P2X receptors are not involved. Based on the pharmacological profile and the fact that acidic conditions are required for ATP to activate the ORCC, we suggest that acidic ATP activates the lymphocyte ORCC via a novel pathway, which is not associated with any previously described purinergic receptors.  相似文献   
14.
This paper describes the tragic case of a young woman who died of cancer of the colon after successfully donating eggs to her younger sister. Although there is no direct link between her operation and the subsequent development of bowel carcinoma, this case imparts a feeling of unease when seen in conjunction with other cases reported during the last few years. It is a reminder that little is known of the long-term consequences of some aspects of assisted conception. Women undergoing ovarian stimulation for themselves or a matched recipient have the right to be advised, in an agreed format, that there is some concern about unproven potential risks from the stimulatory drugs. The safety of egg donors must assume priority over all other considerations, including lack of donors or any moral position. The recent decision by the Human Fertilisation and Embryology Authority (HFEA) to withdraw any form of payment or recompense to egg donors does not seem to us to be based on a balance of scientific advances, patient needs and the ethics of gamete supply. They state that the intention to withdraw payments was implicit in the 1990 Human Fertilisation and Embryology (HFE) Act. However the Act was based on the Warnock report made 6 years earlier. Even in 1990 ovum donation was uncommon and fertility drugs had not yet caused any unease. The Act provided the HFEA with discretionary powers to issue directions so that the future policies would be consistent with any emerging new medical evidence. It is imperative that the HFEA provide convincing evidence on how the current policy of payment to donors harms society, donors or recipients, and how in the UK the new policy will improve medical practice in assisted conception. Successful pilot studies must precede the implementation of any new policy. Failure to do this could cause irreversible harm to the practice of assisted conception using donor gametes, which will ultimately be against the basic aims of the 1990 HFE Act.   相似文献   
15.
A sensitive sandwich enzyme-linked immunosorbent assay (ELISA) that can detect up to 0.5 ng of culture filtrate proteins (CFPs) of Mycobacterium tuberculosis strain H37Ra is described. This detection system features several special characteristics: (i) the use of CFPs from the H37Ra strain of Mycobacterium tuberculosis to generate capture and detection antibodies in rabbits and mice, respectively; (ii) affinity purification of CFP-reactive antibodies and selection of the antibody preparations for best performance in the sandwich ELISA system; and (iii) the use of urine-derived protein preparations for antigen detection. The sandwich ELISA could detect up to 0.5 ng of CFPs of the H37Ra strain of Mycobacterium tuberculosis. The assay did not detect antigens of Escherichia coli, Candida albicans or Saccharomyces cerivisiae but efficiently detected CFP preparations from nine different clinical isolates of Mycobacterium tuberculosis. Significant variations, however, were noted in the relative efficacy of the assay to detect CFPs from different clinical isolates of Mycobacterium tuberculosis. The procedure was utilized for detecting tubercular antigens in urine samples from 29 patients with confirmed (sputum-positive) tuberculosis and from 25 healthy controls. Significant levels of antigen could be detected in 22 of the 29 samples tested. Electronic Publication  相似文献   
16.
A cross-sectional survey of contraceptive practices was conducted among 180 South Asian women aged 16 to 50 years, attending inner-city general practices. Overall prevalence of contraceptive use was 63% and ranged from 70% in South Asian teenagers, to only 50% in women over 30 who had completed their family. Thirteen per cent of women had had a termination of pregnancy Although contraceptive use in this group is increasing, it has not yet reached national levels.  相似文献   
17.
BACKGROUND: Goblet cell carcinoids of the appendix are rare neoplasms with uncertain biological behavior. OBJECTIVE: The aims of our study were to evaluate the immunophenotype of this neoplasm with cell cycle/cell proliferation markers and to understand their histogenesis with ultrastructural analysis using conventional carcinoids as a frame of reference. METHODS: Clinical data and archival pathologic material of all goblet cell carcinoids of the appendix recorded by the Saskatchewan Cancer Registry between 1970 and 1998 were reviewed and evaluated by light microscopy, histochemistry, immunohistochemistry, and electron microscopy. RESULTS: Seven cases of goblet cell carcinoids were identified among 110 cases of conventional carcinoids of the appendix. Histopathology revealed widespread infiltration of the periappendiceal fat in all cases, with extensive perineural invasion. The cells stained strongly positive for mucicarmine, periodic acid-Schiff, periodic acid-Schiff diastase, Alcian blue, cytokeratin, and carcinoembryonic antigen. Most cases were positive for synaptophysin. Increased expression of cell proliferation markers and cell cycle markers was observed. Expression of p53 was strong in one case. Electron microscopy demonstrated the presence of mucinous vacuoles of varying sizes and occasional membrane-bound neuroendocrine granules. CONCLUSIONS: Goblet cell carcinoids of the appendix arise from a pluripotent cell with divergent neuroendocrine and mucinous differentiation. These neoplasms are widely invasive; they demonstrate a high cellular proliferation rate and dysregulation of the cell cycle with up-regulation of cyclin D1 and p21, and down-regulation of p16. Complete removal of the tumor is recommended because of the unpredictable biological behavior of this tumor, which includes delayed local recurrences and lung metastases.  相似文献   
18.
Before November 1989, both the American Association of Blood Banks and the Food and Drug Administration required that thawed cryoprecipitated antihemophilic factor (AHF) should be used immediately or be stored at room temperature and administered within 6 hours. However, in November 1989, the American Association of Blood Banks changed the requirement for storage of thawed cryoprecipitated AHF from room temperature to 1 degree C to 6 degrees C, while the Food and Drug Administration still required thawed cryoprecipitated AHF to be stored at room temperature. The present study was designed to measure and compare the factor VIII activity in 10 bags of thawed cryoprecipitated AHF that were split into aliquots and stored at room temperature and at 1 degree C to 6 degrees C. At 6 and 24 hours after thawing, the mean factor VIII activities (% of normal) of the room temperature-stored cryoprecipitated AHF were 741% and 680% vs 650% and 608% for the 1 degree C- to 6 degrees C-stored cryoprecipitated AHF (P less than .05 at 6 hours and P = .11 at 24 hours). The storage of thawed cryoprecipitated AHF at 1 degree C to 6 degrees C also resulted in precipitation of both factor VIII and fibrinogen. These data show that it is better to store thawed cryoprecipitated AHF at room temperature vs 1 degree C to 6 degrees C for factor VIII activity. These data also suggest that adequate levels of factor VIII are maintained in thawed cryoprecipitated AHF that has been stored at room temperature for up to 24 hours.  相似文献   
19.
Studies from Africa have demonstrated that black people have higher vitamin B12 (cobalamin) levels than do white people. The authors compared healthy white people, black people, and Latin-Americans in the United States. Their study is also the largest in which the effect of race and sex on the cobalamin levels has been examined. Analysis of 233 healthy subjects showed that black people had significantly higher (P less than 0.0001) vitamin B12 levels than did white people. Latin-Americans had levels intermediate between those of white and black people, although their levels were significantly different only in comparison with white people (P = 0.0029). Based on the study of 305 healthy subjects, no sex difference in vitamin B12 levels was noted. Conflicting claims have been made on sex difference in the past. The authors conclude that there is a racial but not a sex difference in vitamin B12 levels in the United States. Like African black people, black people and Latin-Americans in this country have significantly higher vitamin B12 levels than do white people. This finding supports the thesis that genetic factors contribute to the racial differences in vitamin B12 levels.  相似文献   
20.
The distribution of cardiac output (c.o.) was measured by the radioactive microsphere method in rats at different time intervals after the implantation of carrageenanimpregnated sponges. The amount of blood distributed to the developing granulomata increased from day 5 after sponge implantation to day 7, but showed no further increase at day 10. A similar pattern in blood flow was observed in the skin covering the granulomata. Injection of PGE1 (100 ng) into the sponges led to an increase in blood flow, the magnitude of which became gradually larger between days 5 and 10. A similar, though less marked increase in sensitivity to PGE1 was observed in the skin covering the granulomata, PGE1 causing a significant increase in blood flow to the skin on day 10. These changes in sensitivity to exogenous PGE1 may be due to decreasing levels of endogenous PGE and/or maturation of the newly formed blood vessels in the granulation tissue.  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