全文获取类型
收费全文 | 4492篇 |
免费 | 235篇 |
国内免费 | 3篇 |
出版年
2021年 | 30篇 |
2019年 | 28篇 |
2018年 | 39篇 |
2017年 | 29篇 |
2016年 | 49篇 |
2015年 | 77篇 |
2014年 | 102篇 |
2013年 | 336篇 |
2012年 | 223篇 |
2011年 | 214篇 |
2010年 | 134篇 |
2009年 | 144篇 |
2008年 | 230篇 |
2007年 | 221篇 |
2006年 | 231篇 |
2005年 | 257篇 |
2004年 | 264篇 |
2003年 | 262篇 |
2002年 | 260篇 |
2001年 | 110篇 |
2000年 | 86篇 |
1999年 | 94篇 |
1998年 | 70篇 |
1997年 | 65篇 |
1996年 | 50篇 |
1995年 | 52篇 |
1994年 | 51篇 |
1993年 | 42篇 |
1992年 | 74篇 |
1991年 | 75篇 |
1990年 | 57篇 |
1989年 | 67篇 |
1988年 | 67篇 |
1987年 | 52篇 |
1986年 | 30篇 |
1985年 | 51篇 |
1984年 | 50篇 |
1983年 | 45篇 |
1982年 | 49篇 |
1981年 | 44篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1978年 | 27篇 |
1977年 | 30篇 |
1976年 | 25篇 |
1975年 | 27篇 |
1974年 | 24篇 |
1973年 | 17篇 |
1970年 | 12篇 |
1969年 | 12篇 |
排序方式: 共有4730条查询结果,搜索用时 15 毫秒
151.
Hiide Yoshino Nobuyuki Miyatani Megumi Saito Toshio Ariga Alessandra Lugaresi Norman Latov Yasunori Kushi Takeshi Kasama Robert K. Yu 《Journal of neurochemistry》1992,59(5):1684-1691
The gangliosides GM1 and GD1b have recently been reported to be potential target antigens in human motor neuron disease (MND) or motor neuropathy. The mechanism for selective motoneuron and motor nerve impairment by the antibodies directed against these gangliosides, however, is not fully understood. We recently investigated the ganglioside composition of isolated bovine spinal motoneurons and found that the ganglioside pattern of the isolated motoneurons was extremely complex. GM1, GD1a, GD1b, and GT1b, which are major ganglioside components of CNS tissues, were only minor species in motoneurons. Among the various ganglioside species in motoneurons, several were immunoreactive to sera from patients with MND and motor neuropathy. One of these gangliosides was purified from bovine spinal cord and characterized as N-glycolylneuraminic acid-containing GM1 [GM1(NeuGc)] by compositional analysis, fast atom bombardment mass spectra, and the use of specific antibodies. Among seven sera with anti-GM1 antibody activities, five sera reacted with GM1(NeuGc) and two did not. Two other gangliosides, which were recognized by another patient's serum, appeared to be specific for motoneurons. We conclude that motoneurons contained, in addition to the known ganglioside antigens GM1 and GD1b, other specific ganglioside antigens that could be recognized by sera from patients with MND and motor neuropathy. 相似文献
152.
Genetic Manipulation of the Extent of Desaturation of Fatty Acids in Membrane Lipids in the Cyanobacterium Synechocystis PCC6803 总被引:1,自引:0,他引:1
Wada Hajime; Gombos Zoltan; Sakamoto Toshio; Murata Norio 《Plant & cell physiology》1992,33(5):535-540
The desA gene of the cyanobacterium, Synechocystis PCC6803,is responsible for the desaturation of fatty acids at the 相似文献
153.
Toshio Sugimoto Tsutomu Kawasaki Tomohiko Kato Robert F. Whittier Daisuke Shibata Yukio Kawamura 《Plant molecular biology》1992,20(4):743-747
A full-length cDNA encoding a subunit of phosphoenolpyruvate carboxylase (PEPC) was isolated from a developing seed expression library of the C3 plant Glycine max. The corresponding mRNA is present at similar levels in leaf, stem, root and developing seed. Two potential start codons exist, and the activity of protein initiated from the first such codon could be subject to regulation by protein kinase. Sequence comparison shows a similar upstream start codon in the case of the Ppc2 gene from Mesembryanthemum crystallinum, previously assumed to lack the sequences necessary for phosphorylation. The soybean encoded protein tends to resemble other C3-type PEPC proteins more closely than those implicated in C4 or crassulacean acid metabolism. 相似文献
154.
A Naito Y Kitamura H Yoshikura 《Biochemical and biophysical research communications》1991,174(1):305-312
Relative orientation of recombination substrates, neo gene, strongly influenced homologous recombination events in a bovine papillomavirus shuttle vector. Between direct repeats, recombination occurred at a high frequency while between inverted repeats, it was rare. Double strand break near the mutation site increased the recombination frequency between inverted repeats but not between direct repeats. Formation of long heteroduplex as a recombination intermediate may explain this apparently paradoxical phenomenon. 相似文献
155.
Data from the North Pacific sperm whale (Physeter catodon Linnaeus, 1758) fishery were examined for a possible density dependent change in growth during 40 yr harvesting after World War II. Early in this period males from the eastern stock were 16.8 m or less in length. By the early 1970s the largest males in the catch exceeded 16.8 m in length and reached 18.9 m in the late 1970s. The proportion of males measuring over 16.8 m, among sexually mature males (≥14.0 m), increased from 0 to >20% during the 1970s. Increases in the maximum size of males were possibly preceded by a change in the frequency distribution of body lengths in the middle 1960s when only 10% of the postwar catch had been taken. Testis weights suggested an increase in body length at sexual maturity. Two of the three putative North Pacific stocks showed similar growth changes. Adult males taken in the Bering Sea did not show such changes during the exploitation which ended in 1972 because of overfishing. Females showed no detectable change in body size. It is concluded that: (1) density dependent effects on male growth are greater before sexual maturity than after it, (2) males may show density dependent changes even at a population level above 90% of the carrying capacity, (3) polygynous males acquire more mates and realize higher reproductive success because of increased body size, and (4) females appear to maximize production by maturing earlier and shortening calving intervals in response to density change. 相似文献
156.
Dissociation of hydroxylase and lyase activities by site-directed mutagenesis of the rat P45017 alpha. 总被引:1,自引:0,他引:1
Site-directed mutagenesis of the arginine-rich region within the putative active site of the rat testicular P45017 alpha (17 alpha-hydroxylase cytochrome P-450, the product of P450XVII gene) was performed to identify specific amino acids that contribute to either the hydroxylase or lyase activities catalyzed by this enzyme. The conversion of Arg346 to alanine differentially abolished lyase activity without affecting hydroxylase activity, resulting in an accumulation of the 17 alpha-hydroxylated intermediate, and partial lyase activity was recovered by conversion of this mutant to Lys346. Similar results were obtained with the conversion of Arg357 to alanine, although this mutant also diminished hydroxylase activity, and full lyase and hydroxylase activities were recovered with a lysine in this position. Major reductions in hydroxylase activity were apparent with the conversion of Arg363 to Ala, and this inhibition was reversed by a lysine at position 363. In contrast, differential effects were not observed with the mutants Arg361 Ala, Arg361 Lys, or Tyr334Phe. Both mutations at the Arg361 position resulted in a total loss of hydroxylase and lyase activities, and mutation at the Tyr334 position had no effect on either activity. The identification of specific amino acids that are essential for either the hydroxylase or lyase reaction indicates that the steroid substrate-protein interaction changes during the course of the two consecutive reactions and reveals the potential for separation of the two activities by chemical and biological modulators within the active site region of the P45017 alpha. 相似文献
157.
158.
159.
Li-Chun Huang Cheng-Kuo Hsiao Shu-Huey Lee Bau-Lian Huang Toshio Murashige 《In vitro cellular & developmental biology. Plant》1992,28(1):30-32
Summary Repeated grafting of 0.2-cm shoot tips from fruiting-age trees ofCitrus reticulata Blanco ‘Ponkan’ mandarin andC. sinensis Osbeck ‘Liu Tseng’ sweet orange onto freshly germinated ‘Troyer’ citrange [Poncirus trifoliata (L.) Raf. X.C. sinensis Osbeck] seedlings in vitro resulted in progressive restoration of rooting competence and vigor of regenerated roots and shoots.
The restored traits were retained through the course of the investigation and suggested a phase reversal phenomenon. 相似文献