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   8587篇
  免费   814篇
  国内免费   1532篇
  2024年   26篇
  2023年   175篇
  2022年   241篇
  2021年   603篇
  2020年   443篇
  2019年   532篇
  2018年   461篇
  2017年   366篇
  2016年   422篇
  2015年   630篇
  2014年   762篇
  2013年   689篇
  2012年   912篇
  2011年   750篇
  2010年   511篇
  2009年   425篇
  2008年   424篇
  2007年   393篇
  2006年   338篇
  2005年   306篇
  2004年   211篇
  2003年   176篇
  2002年   178篇
  2001年   139篇
  2000年   139篇
  1999年   115篇
  1998年   89篇
  1997年   58篇
  1996年   51篇
  1995年   42篇
  1994年   50篇
  1993年   31篇
  1992年   28篇
  1991年   30篇
  1990年   29篇
  1989年   30篇
  1988年   20篇
  1987年   22篇
  1986年   18篇
  1985年   14篇
  1984年   11篇
  1983年   9篇
  1982年   5篇
  1981年   3篇
  1980年   3篇
  1979年   3篇
  1977年   3篇
  1973年   3篇
  1970年   2篇
  1968年   2篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
应用酶联免疫吸附试验检测马铃薯卷叶病毒   总被引:2,自引:0,他引:2  
以辣根过氧化物酶标记马铃薯卷叶病毒抗体,采用双抗体夹心ELISA方法鉴定了马铃薯和洋酸浆的茎、叶、根及马铃薯块茎中的马铃薯卷叶病毒(Potato Leafroll Virus,PLRV),结果表明,对提纯的PLRV可测出的最低浓度为25ng/ml,当包被抗体浓度为40μg/ml、酶标记抗体稀释度为1/120时,可测出马铃薯茎、叶和根汁液中的PLRV,感染PLRV的洋酸浆茎、叶和根汁液的消光值,均比无病对照者高二倍以上,虽然感染PLRV的马铃薯休眠块茎维管束组织汁液的消光值高于无病毒对照,且脐部维管束组织消光值高于顶端,但测定打破休眠的感病块茎顶端维管束组织的阳性结果更为可靠和明显。  相似文献   
22.
Guinea-pigs were immunized with a defined and highly potent aspermatogenic antigen, G75m, and the occurrence of orchitis was correlated with (1) cell-mediated immune response to G75m, determined by lymph node cell proliferation and by secretion of macrophage migration inhibitory factor (MIF) by peritoneal exudate cells, and (2) humoral antibodies to G75m and to cell surface antigens of guinea-pig testicular cells, by radioimmunometric assays. A consistent temporal relationship between cell-mediated immune responses and disease was found: lymph node cell proliferation was positive by Day 4, followed 3 days later by maximum secretion of MIF, and orchitis lesions were manifest on Day 10. In contrast, maximal IgG antibodies to G75m or to the surface antigens of spermatozoa/testicular cells were detected at a time when cell-mediated immune responses and active testicular lesions had subsided. In individual animals, lymph node cell proliferation increased with severity of orchitis, while MIF secretion by peritoneal cells increased with orchitis only late in the disease. Early in disease, MIF response showed a negative correlation with orchitis. Moreover, peritoneal injection of oil reduced the incidence of early lymph node cell proliferative responses, and delayed the onset of testicular disease. These findings are consistent with competition between different inflammatory sites for recently antigen-activated T lymphocytes. We conclude that (1) the development of orchitis correlates with cell-mediated immune responses to purified aspermatogenic antigens but not with IgG antibody responses, and (2) when the same animal is used to assess different aspects of cellular immunity and autoimmune disease, one study may significantly influence the other.  相似文献   
23.
24.
25.
采用性腺败育(GD不育)作为标准检定方法。对我国20个地方的黑腹果蝇的P因子活性和细胞型进行了测定。结果表明我国北部沿海城市为Q型;南部沿海和内地皆为M型。各地的M品系所产生的GD不育能力各不相同,但表现出与地理位置相关的梯度变化。这一变化规律为研究我国黑腹果蝇的P因子起源及P和M品系的形成提供了重要的理论依据。  相似文献   
26.
中国拟盘多毛孢属真菌的七个新组合   总被引:4,自引:4,他引:0  
作者按照Steyaert(1949)和Sutton(1980)的分类观点,对1987—1988年从我国广西、江西、浙江等地采集的Pestalotiopsis属真菌进行了研究,确认了拟盘多毛孢属真菌的7个新组合种,即Pestalotiopsis carveri(Guba)comb nov.,Pestalotiopsis elasticae(Koord.)comb.nov.,Pestalotiopsis langloisii(Guba)comb.nov.,Pestalotiopsis oleandri(Guba)comb.nov.,Pestalotiopsis sinensis(shen)comb.nov.,Pestalotiopsis sydowiana(Bres.)comb.nov.和Pestalotiopsis zahlbruckneriana(Bres.)comb.nov.  相似文献   
27.
Familial hypoalphalipoproteinemia (hypoalpha), characterized by a decreased high density lipoprotein level, is associated with an increased incidence of premature cardiovascular disease. Restriction fragment length polymorphism analysis of genomic DNA has detected a polymorphism for the PstI restriction endonuclease near the apoA-I gene, with either a 2.2 or a 3.3 kb fragment. The latter has been previously found to occur with significantly higher frequency in probands of families with familial hypoalpha. ApoA-I was isolated from three unrelated subjects with familial hypoalpha and the 3.3 kb PstI polymorphism of the apoA-I gene, and from normal control subjects. The apoA-I from the hypoalpha subjects was structurally normal as determined by amino acid analysis and by two-dimensional gel electrophoresis. When normal apoA-I and hypoalpha apoA-I were simultaneously injected into either normal controls or hypoalpha subjects, both forms of apoA-I were catabolized at the same rate in the same subject, indicating that the hypoalpha apoA-I is also metabolically normal. Analysis of the kinetics of metabolism of apoA-I in the hypoalpha subjects, compared to the normal controls, revealed that the reduced plasma levels of apoA-I were due to an increased apoA-I fractional catabolic rate, and that the synthetic rate was normal. Based on these results, we conclude that the apoA-I gene in these hypoalpha subjects is normal, and the PstI polymorphism near the apoA-I gene, which is associated with familial hypoalpha, is likely to be a marker for a mutant gene closely linked to, but not in, the apoA-I gene.  相似文献   
28.
About 60% of both Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) is due to deletions of the dystrophin gene. For cases with a deletion mutation, the "reading frame" hypothesis predicts that BMD patients produce a semifunctional, internally deleted dystrophin protein, whereas DMD patients produce a severely truncated protein that would be unstable. To test the validity of this theory, we analyzed 258 independent deletions at the DMD/BMD locus. The correlation between phenotype and type of deletion mutation is in agreement with the "reading frame" theory in 92% of cases and is of diagnostic and prognostic significance. The distribution and frequency of deletions spanning the entire locus suggests that many "in-frame" deletions of the dystrophin gene are not detected because the individuals bearing them are either asymptomatic or exhibit non-DMD/non-BMD clinical features.  相似文献   
29.
斜胸叶蝉属一新种(同翅目:叶蝉总科:耳叶蝉科)   总被引:1,自引:0,他引:1  
葛钟麟  蔡平 《动物学报》1992,38(2):136-138
本文记述耳叶蝉科斜胸叶蝉属一新种:黄缘斜胸叶蝉Epiclinata flavomarinata sp.nov.。标本采自我国西藏。文中描述了新种的外部形态及雄性外生殖器构造特征,并与近似种进行比较,附有主要特征图。模式标本保存于中国科学院动物研究所。  相似文献   
30.
丁型肝炎病毒感染东方土拔鼠的实验研究   总被引:2,自引:0,他引:2  
金志宏  杨波 《病毒学报》1990,6(1):74-76
  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