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   4734篇
  免费   549篇
  国内免费   6篇
  5289篇
  2023年   35篇
  2022年   55篇
  2021年   125篇
  2020年   72篇
  2019年   81篇
  2018年   93篇
  2017年   92篇
  2016年   157篇
  2015年   226篇
  2014年   232篇
  2013年   239篇
  2012年   341篇
  2011年   328篇
  2010年   229篇
  2009年   192篇
  2008年   291篇
  2007年   276篇
  2006年   288篇
  2005年   241篇
  2004年   223篇
  2003年   212篇
  2002年   181篇
  2001年   76篇
  2000年   58篇
  1999年   64篇
  1998年   47篇
  1997年   30篇
  1996年   41篇
  1995年   38篇
  1994年   30篇
  1993年   29篇
  1992年   41篇
  1991年   40篇
  1990年   26篇
  1989年   32篇
  1988年   29篇
  1987年   27篇
  1986年   33篇
  1985年   24篇
  1984年   31篇
  1983年   17篇
  1982年   25篇
  1981年   15篇
  1980年   26篇
  1979年   15篇
  1978年   23篇
  1977年   24篇
  1976年   18篇
  1974年   20篇
  1971年   16篇
排序方式: 共有5289条查询结果,搜索用时 15 毫秒
11.
12.
A study of factors influencing genetic counseling attendance rate has been conducted in the Bouches-du-Rh?ne area, in the south of France. In this area, a birth defects monitoring system (Eurocat n. 22) annually covers 23,000 births. All the genetic services are delivered by only one genetic center located in Marseilles, and the data collected are computerized. The comparison of these two data bases gives an opportunity to estimate the rate of genetic counseling attendance after the occurrence of an affected stillbirth or live birth. Among the parents of 358 infants born in 1983-84 in this area with a pathology requiring genetic counseling, 226 (63 per cent) attended the Genetic Center within the first year after birth. The rate of attendance is statistically higher (p less than 0.01) for the parents who had a stillbirth (78 per cent) than for those who had a live birth (57 per cent). It is also higher (p less than 0.01) for the Marseilles maternities group (68 per cent) than for the group outside Marseilles (50 per cent). The referral delays are also analyzed according to malformation etiology and to viability of the child by the eighth day of life. Besides evaluating a particular genetic center's effectiveness in diffusing information to the public concerned, this work shows that couples' request is strongly dependent on a psychological need.  相似文献   
13.
L Blanco  A Bernad    M Salas 《Journal of virology》1988,62(11):4167-4172
The transition step from the p3-dAMP initiation complex to the first elongated products, p3-(dAMP)2 and p3-(dAMP)3, requires a dATP concentration higher than that needed for the initiation reaction or for the further elongation of the p3-(dAMP)3 complex. The elongation in phi 29 DNA-protein p3 replication in vitro was strongly inhibited by salt. Under inhibitory salt concentration, the viral protein p6 greatly stimulated phi 29 DNA-protein p3 replication. The effect of protein p6 was not on the rate of elongation but on the amount of elongated product, stimulating the transition from initiation to formation of the first elongation products.  相似文献   
14.
Pneumocystis carinii shows DNA homology with the ustomycetous red yeast fungi   总被引:11,自引:0,他引:11  
Pneumocystis carinii causes life-threatening pneumonia in T-lymphocyte-immunodeficient subjects in transplant and oncology units or with acquired immune deficiency syndrome (AIDS). Recent DNA homology studies show P. carinii to be a fungus. To investigate the biology and epidemiology of this parasite further, we elected to determine for it a more precise taxonomic assignment within the fungal kingdom. We screened a wide range of organisms representing the major orders of fungi using DNA amplification and subsequently sequenced a portion of the mitochondrial gene encoding the large subunit ribosomal RNA. Our data show that the opportunistic pulmonary pathogen P. carinii is closely related to the ustomycetous red yeast fungi, a group which includes organisms that are extensively distributed throughout the environment and which release many widely dispersed airborne spores.  相似文献   
15.
Summary The cell wall-associated proteinase from Lactococcus lactis subsp. cremoris SK11 was partially purified and incubated with s1-casein for various times up to 48 h. Sixteen trifluoroacetic acid-soluble oligopeptide hydrolysis products were identified by determination of the aminp acid sequence. Eleven of these oligopeptides originated from the 78-residue sequence comprising the C-terminal region of s1-casein and were present among the products after the first 60 min of digestion. Three oligopeptides from the N-terminal region and two others from the central region of the s1-casein sequence were also present among the early digestion products although in smaller amounts than most of the oligopeptides from the C-terminal region. No cleat consensus sequence of amino acid residues surrounding the cleavage sites could be identified.Offprint requests to: G. G. Pritchard  相似文献   
16.
17.
Summary Serum-free supernatants from the human melanoma cell line G361 contain a factor that can potently suppress the generation of tumouricidal lymphokine-activated killer (LAK) cells in response to interleukin-2. To characterise the suppressive factor of tumour origin we performed a number of physicochemical and functional comparisons with another immunosuppressive protein, transforming growth factor (TGF). The bioactivity of tumour-derived suppressor factor (TDSF), assayed by suppression of LAK cell generation, was unaffected by a reducing agent but lost when denatured with a chaotropic agent. In contrast, TGF was inactivated by reduction but not denaturation. TDSF lost bioactivity in conditions of pH less than 4, whereas TGF showed no loss of activity. The TDSF moiety has an estimated pI of 4.3 and a molecular mass of 69–87 kDa. This differs from published values of pI 9.5, and 25 kDa molecular mass for TGF. Anti-TGF antiserum reversed the effects of TGF but did not affect the suppression of LAK cell generation caused by TDSF. These findings provide compelling evidence that the TDSF moiety is not TGF, and may be a novel immunoregulatory cytokine.  相似文献   
18.
19.
Julian C. Lee 《Oecologia》1986,69(2):207-212
Summary This study examines the idea that variation in forelimb length among male anurans influences reproductive success, and does so independently of body size. Analyses of covariance and multivariate analyses of morphological data for five species of explosives breeders are used to test the prediction that for species in which male-male displacements contribute to variation in male reproductive success, amplectant males have longer forelimbs than do non-amplectant males at any body length. The findings for four of five species are in agreement with expectation. The results lend support to the suggestion that for explosive-breeding anurans, the large-male mating advantage may not be a consequence of large body size per se, but rather is due to the fact that large males have longer forelimbs with which to grasp females securely during amplexus and thus resist displacements by competing males.  相似文献   
20.
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