全文获取类型
收费全文 | 868305篇 |
免费 | 103512篇 |
国内免费 | 891篇 |
出版年
2018年 | 7392篇 |
2016年 | 10031篇 |
2015年 | 14396篇 |
2014年 | 16967篇 |
2013年 | 23649篇 |
2012年 | 26933篇 |
2011年 | 27437篇 |
2010年 | 18292篇 |
2009年 | 16936篇 |
2008年 | 24395篇 |
2007年 | 25436篇 |
2006年 | 23867篇 |
2005年 | 22964篇 |
2004年 | 22886篇 |
2003年 | 21804篇 |
2002年 | 21049篇 |
2001年 | 35968篇 |
2000年 | 36274篇 |
1999年 | 29169篇 |
1998年 | 11018篇 |
1997年 | 11256篇 |
1996年 | 10756篇 |
1995年 | 10334篇 |
1994年 | 10024篇 |
1993年 | 10036篇 |
1992年 | 25079篇 |
1991年 | 24863篇 |
1990年 | 24437篇 |
1989年 | 23712篇 |
1988年 | 22125篇 |
1987年 | 21145篇 |
1986年 | 19928篇 |
1985年 | 20047篇 |
1984年 | 16773篇 |
1983年 | 14699篇 |
1982年 | 11233篇 |
1981年 | 10515篇 |
1980年 | 9791篇 |
1979年 | 16291篇 |
1978年 | 12997篇 |
1977年 | 11760篇 |
1976年 | 11154篇 |
1975年 | 12582篇 |
1974年 | 13433篇 |
1973年 | 13049篇 |
1972年 | 12095篇 |
1971年 | 10872篇 |
1970年 | 9365篇 |
1969年 | 8992篇 |
1968年 | 8217篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
223.
224.
225.
226.
A new gas-liquid chromatographic method was developed for the determination of diethylether in whole blood. Ether was quantitated by peak area ratio analysis with n-propanol as the internal standard using a flame ionization detector. Blood ether concentrations were determined in cats undergoing inhalational anesthesia by ether in oxygen. In normal spontaneously breathing cats, anesthesia began at ether concentrations of about 0.6 g/l, and respiratory arrest occurred at 2.4 g/l and above. Mean arterial blood pressure was well maintained throughout the entire anesthetic range. In spinal artificially respired animals, mean arterial blood pressure correlated inversely with blood ether concentration. The data suggest that decline in blood pressure may be a useful sign of ether toxicity in spinal cats. 相似文献
227.
228.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed. 相似文献
229.
ABSTRACT The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship. 相似文献
230.
Ffh is a component of a bacterial ribonucleoprotein complex homologous to the signal recognition particle (SRP) of eukaryotes. It comprises three domains that mediate both binding to the hydrophobic signal sequence of the nascent polypeptide and the GTP-dependent interaction of Ffh with a structurally homologous GTPase of the SRP receptor. The X-ray structures of the two-domain 'NG' GTPase of Ffh in complex with Mg2+GDP and GDP have been determined at 2.0 A resolution. The structures explain the low nucleotide affinity of Ffh and locate two regions of structural mobility at opposite sides of the nucleotide-binding site. One of these regions includes highly conserved sequence motifs that presumably contribute to the structural trigger signaling the GTP-bound state. The other includes the highly conserved interface between the N and G domains, and supports the hypothesis that the N domain regulates or signals the nucleotide occupancy of the G domain. 相似文献