全文获取类型
收费全文 | 3147篇 |
免费 | 185篇 |
国内免费 | 1篇 |
专业分类
3333篇 |
出版年
2022年 | 17篇 |
2021年 | 34篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 26篇 |
2017年 | 24篇 |
2016年 | 34篇 |
2015年 | 90篇 |
2014年 | 110篇 |
2013年 | 158篇 |
2012年 | 145篇 |
2011年 | 187篇 |
2010年 | 102篇 |
2009年 | 103篇 |
2008年 | 156篇 |
2007年 | 187篇 |
2006年 | 163篇 |
2005年 | 162篇 |
2004年 | 159篇 |
2003年 | 153篇 |
2002年 | 137篇 |
2001年 | 110篇 |
2000年 | 91篇 |
1999年 | 73篇 |
1998年 | 34篇 |
1997年 | 43篇 |
1996年 | 43篇 |
1995年 | 25篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 71篇 |
1991年 | 48篇 |
1990年 | 44篇 |
1989年 | 52篇 |
1988年 | 33篇 |
1987年 | 47篇 |
1986年 | 37篇 |
1985年 | 50篇 |
1984年 | 35篇 |
1983年 | 36篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 27篇 |
1978年 | 15篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1972年 | 13篇 |
1971年 | 11篇 |
排序方式: 共有3333条查询结果,搜索用时 15 毫秒
1.
We have previously shown that replacing the P1-site residue (Ala) of chicken ovomucoid domain 3 (OMCHI3) with a Met or Lys results in the acquisition of inhibitory activity toward chymotrypsin or trypsin, respectively. However, the inhibitory activities thus induced are not strong. In the present study, we introduced additional amino acid replacements around the reactive site to try to make the P1-site mutants more effective inhibitors of chymotrypsin or trypsin. The amino acid replacement Asp-->Tyr at the P2' site of OMCHI3(P1Met) resulted in conversion to a 35000-fold more effective inhibitor of chymotrypsin with an inhibitor constant (K(i)) of 1. 17x10(-11) M. The K(i) value of OMCHI3(P1Met, P2'Ala) indicated that the effect on the interaction with chymotrypsin of removing a negative charge from the P2' site was greater than that of introducing an aromatic ring. Similarly, enhanced inhibition of trypsin was observed when the Asp-->Tyr replacement was introduced into the P2' site of OMCHI3(P1Lys). Two additional replacements, Asp-->Ala at the P4 site and Arg-->Ala at the P3' site, made the mutant a more effective inhibitor of trypsin with a K(i) value of 1. 44x10(-9) M. By contrast, Arg-->Ala replacement at the P3' site of OMCHI3(P1Met, P2'Tyr) resulted in a greatly reduced inhibition of chymotrypsin, and Asp-->Ala replacement at the P4 site produced only a small change when compared with a natural variant of OMCHI3. These results clearly indicate that not only the P1-site residue but also the characteristics, particularly the electrostatic properties, of the amino acid residues around the reactive site of the protease inhibitor determine the strength of its interactions with proteases. Furthermore, amino acids with different characteristics are required around the reactive site for strong inhibition of chymotrypsin and trypsin. 相似文献
2.
3.
Echolocation sounds and hearing of the greater Japanese horseshoe bat (Rhinolophus ferrumequinum nippon) 总被引:1,自引:0,他引:1
Ikuo Taniguchi 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,156(2):185-188
Summary The relationship between the orientation sounds and hearing sensitivity in the greater Japanese horseshoe bat,Rhinolophus ferrumequinum nippon was studied.An orientation pulse consisted of a constant frequency (CF) component followed by a short downward frequency-modulated (FM) component. Sometimes, an initial upward FM component preceded the CF component. Duration of pulses was about 30 ms and the CF of resting pulses (RF) averaged 65.5 kHz. The best frequency (BF) at the lowest threshold in audiograms as measured by the pinna reflex averaged 66.1 kHz. Audiograms showed remarkable sharp cut-offs on both sides near the BF. The frequency difference between the BF and the RF was about 0.6 kHz, and the RF was always below the BF. The values of RF and BF were characteristically different from those of the European subspecies,Rhinolophus ferrumequinum ferrumequinum.Abbreviations
BF
best frequency
-
CF
constant frequency
-
FM
frequency modulated
-
RF
resting frequency 相似文献
4.
5.
Centrifugal filtration through a double layer of silicone oil was applied to determine the intermembrane space of organelles enclosed by double envelope membranes, i.e. proplastids, chloroplasts, mitochondria and amyloplasts. The organelles, capable of transporting adenylates by an adenylate translocator located in the inner envelope membrane, were incubated with increasing concentrations of adenylates while maintaining their specific radioactivities constant. Intermembrane spaces were estimated by extrapolation of radioactivities recovered after filtration of the organelles. The values estimated were compared to those obtained employing the classical method measuring the intake of [14C]-sucrose and [14C]-sorbitol which are impermeable to the inner membranes of organelles. The intermembrane space determined by the present method was shown to be uniformly smaller than the sucrose-permeable space which was always smaller than the sorbitol-permeable space. 相似文献
6.
To reveal the difference of molecular property between structurallysimilar odorless and odoriferous musk compounds, 10 pairs ofbenzenoids (monocyclic-, dicyclic- and tricyclic-) were examined.Molecular structures of all compounds were optimized by MNDO(modified neglect of diatomic differential overlap) consideringconformation. Parameters effective in discriminating two groups,group A of 10 odorless compounds and group B of 10 musk odorcompounds, were searched from 34 candidate parameters by adaptiveleast squares. The best three parameters found were log P value(octanol/water partition coefficient), the longest side lengthof hexahedron circumscribing a molecule, and the parameter whichexpresses structural hindrance to the functional group whena molecule approaches the receptor site. The two groups of compoundswere completely discriminated using these three parameters. 相似文献
7.
Primary structures of two types of alpha-subunit of rat brain Na+,K+,-ATPase deduced from cDNA sequences 总被引:2,自引:0,他引:2
Y Hara O Urayama K Kawakami H Nojima H Nagamune T Kojima T Ohta K Nagano M Nakao 《Journal of biochemistry》1987,102(1):43-58
A rat brain cDNA library was screened by using as a probe a fragment of cDNA encoding the alpha-subunit of human Na+,K+-ATPase. Two different cDNA clones were obtained and analyzed. One of them was concluded to be a cDNA encoding the alpha-subunit of the weakly ouabain-sensitive rat kidney-type Na+,K+-ATPase. The deduced amino acid sequence consists of 1,018 amino acids. The alpha-subunit of the rat kidney-type Na+,K+-ATPase shows 97% homology in amino acid sequence with the alpha-subunit of human, sheep, or pig enzyme and 87% with that of Torpedo. Based on a comparison of the amino acid sequence at the extracellular domain of the alpha-subunit between weakly ouabain-sensitive rat kidney-type enzyme and the ouabain-sensitive human, sheep, pig, or Torpedo enzyme, it was proposed that only two significant amino acid replacements are unique to the rat kidney-type alpha-subunit. Another cDNA clone obtained showed 72% homology in nucleotide sequence with the former cDNA coding the alpha-subunit of the rat kidney-type Na+,K+-ATPase and the deduced amino acid sequence exhibited 85% homology with that of the alpha-subunit of rat kidney-type Na+,K+-ATPase. 相似文献
8.
Porcine polymorphonuclear leukocyte NADPH-cytochrome c reductase generates superoxide in the presence of cytochrome b559 and phospholipid 总被引:1,自引:0,他引:1
F Sakane H Kojima K Takahashi J Koyama 《Biochemical and biophysical research communications》1987,147(1):71-77
NADPH-cytochrome c reductase and cytochrome b559 were purified from the membrane fraction of phorbol myristate acetate-stimulated porcine polymorphonuclear leukocytes. The highly purified reductase oxidized NADPH and generated superoxide when combined with partially purified cytochrome b559 in the presence of phosphatidylcholine. In the same system, but under the anaerobic condition, the reductase was found to reduce cytochrome b559. 相似文献
9.
Synthesis of Collagen-Like Proteins in Embryonic Organs of the Sea Urchin, Hemicentrotus pulcherrimus 总被引:1,自引:1,他引:0
Hazime Mizoguchi Akiko Fujiwara Ikuo Yasumasu 《Development, growth & differentiation》1989,31(2):189-196
In sea urchin embryos exposed to 14 C-proline at 20°C for 3 hr at the gastrula, prism or pluteus stage, 14 C-radioactivity was found in hot acid-extractable proteins, in which more than 4% of the radioactivity was detectable in hydroxyproline residues. In these embryos, 14 C-radioactivity in collagen-like proteins was found in the archenteron, spicule and embryo-wall cells. The rate of synthesis of collagen-like proteins was highest in the archenteron in the mid-gastrula stage, in the embryo-wall cells in the prism stage and in the spicule in the pluteus stage. The rate of synthesis decreased in the archenteron and increased in embryo-wall cells in the period between the mid- and late-gastrula stages, when the rate of synthesis in the spicule was quite low. Thereafter, the rate decreased slightly in the embryo-wall cells, was maintained in archenteron and increased markedly in the spicule. The rates of synthesis of collagen-like proteins are high in these embryonic organs at stages at which development and growth respectively, occur in embryos. Therefore, synthesis of collagen-like proteins probably supports morphogenesis in these embryonic organs. 相似文献
10.
Expression of active alpha-3 subunit of rat brain Na+,K+-ATPase from the messenger RNA injected into Xenopus oocytes 总被引:2,自引:0,他引:2
Y Hara M Ohtsubo T Kojima S Noguchi M Nakao M Kawamura 《Biochemical and biophysical research communications》1989,163(1):102-105
Cloned cDNA encoding the so-far uncharacterized alpha-3 subunit of rat brain Na+,K+-ATPase (Hara et al. (1987) J. Biochem. 102, 43-58, Shull et al. (1986) Biochemistry 25, 8125-8132) was incorporated into a vector carrying the SP6 promoter. The mRNA produced in vitro was injected into Xenopus oocytes with the mRNA encoding the Na+,K+-ATPase beta subunit of Torpedo electroplax. Increased Na+,K+-ATPase activity in the oocyte membrane was observed. This newly expressed activity was inhibited by ouabain (Ki = 1.5 x 10(-7) M), suggesting that the alpha-3 subunit of rat brain Na+,K+-ATPase is a highly ouabain-sensitive catalytic subunit. 相似文献