全文获取类型
收费全文 | 2045篇 |
免费 | 135篇 |
出版年
2022年 | 10篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 29篇 |
2015年 | 48篇 |
2014年 | 68篇 |
2013年 | 154篇 |
2012年 | 108篇 |
2011年 | 105篇 |
2010年 | 48篇 |
2009年 | 50篇 |
2008年 | 97篇 |
2007年 | 78篇 |
2006年 | 73篇 |
2005年 | 87篇 |
2004年 | 81篇 |
2003年 | 92篇 |
2002年 | 79篇 |
2001年 | 80篇 |
2000年 | 91篇 |
1999年 | 64篇 |
1998年 | 23篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 7篇 |
1993年 | 17篇 |
1992年 | 59篇 |
1991年 | 46篇 |
1990年 | 43篇 |
1989年 | 50篇 |
1988年 | 40篇 |
1987年 | 27篇 |
1986年 | 30篇 |
1985年 | 39篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 16篇 |
1974年 | 8篇 |
1973年 | 12篇 |
排序方式: 共有2180条查询结果,搜索用时 15 毫秒
1.
A spectrophotometric method for inorganic phosphate determination in the presence of thiol compounds is described. Thiol compounds, which interfere with the measurement of inorganic phosphate by a modification of the method of Gomori, are removed by carboxymethylation by iodoacetate prior to the formation and reduction of phosphomolybdate complex. A linear standard curve is obtained by this method, and the method is suitable for the assay of a phosphate-releasing enzyme when the measurement must be performed in the presence of thiol compounds. 相似文献
2.
Alexandre Suire Lynne A. Isbell Laura R. Bidner Yushin Shinoda Munemitsu Akasaka Akiko Matsumoto‐Oda 《American journal of primatology》2021,83(1)
For diurnal nonhuman primates, shifting among different sleeping sites may provide multiple benefits such as better protection from predators, reduced risk of parasitic infection, and closer proximity to spatially and temporally heterogeneous food and water. This last benefit may be particularly important in sleeping site selection by primates living in savanna‐woodlands where rainfall is more limited and more seasonally pronounced than in rainforests. Here, we examined the influence of rainfall, a factor that affects food and water availability, on the use of sleeping sites by anubis baboons (Papio anubis) over two 13‐month study periods that differed in rainfall patterns. We predicted that during wet periods, when food and water availability should be higher, the study group would limit the number of sleeping sites and would stay at each one for more consecutive nights than during dry periods. Conversely, we predicted that during dry periods the group would increase the number of sleeping sites and stay at each one for fewer consecutive nights as they searched more widely for food and water. We also predicted that the group would more often choose sleeping sites closer to the center of the area used during daytime (between 07:00 and 19:00) during wet months than during dry months. Using Global Positioning System data from collared individuals, we found that our first prediction was not supported on either monthly or yearly timescales, although past monthly rainfall predicted the use of the main sleeping site in the second study period. Our second prediction was supported only on a yearly timescale. This study suggests that baboons’ choice of sleeping sites is fluid over time while being sensitive to local environmental conditions, one of which may be rainfall. 相似文献
3.
Monoclonal antibodies against chick embryonic beta-galactoside-binding lectin were obtained. One of the monoclonal antibodies was ineffective in Western blotting and seemed to be unable to bind the SDS-denatured lectin. When the native lectin was dotted on a nitrocellulose filter and subjected to denaturation by treatment with SDS, urea or heat, binding of this antibody no longer occurred, though other monoclonal antibodies bound normally. This antibody seems to have been raised against an epitope which is destroyed upon denaturation. 相似文献
4.
The effects of certain physicochemical parameters on the formation and stability of a complex between Streptomyces proteinaceous metalloprotease inhibitor (SMPI) and thermolysin were investigated. SMPI had its lowest Ki value at a pH of around 6.5 (similar to the pH dependence of the kcat/K(m) of thermolysin catalysis), reflecting the splitting mechanism of the SMPI inhibition of thermolysin. This Ki increased with an increase in pressure, and in (Ki-1) was almost linear with respect to pressure. The volume of the reaction (delta Vcomp), which is the volume change accompanying enzyme-inhibitor complex formation, was calculated as +8.1 +/- 0.3 mL.mol-1, which has a sign opposite to delta Vcomp for neutral peptide inhibitors and acyl-peptide substrates. The temperature dependence of Ki-1 gave the reaction enthalpy (delta Hcomp) and reaction entropy (delta Scomp) of the complex formation as 34.6 +/- 1.4 kJ.mol-1 and 298 +/- 5 J.mol-1.K-1, respectively. These positive reaction volumes and reaction entropies were related to the electrostatic interactions and ionic strength dependence of Ki which corresponded to the key ionic interaction during complex formation. Complex formation with SMPI stabilized thermolysin against pressure perturbation as observed by the changes in the Trp fluorescence of thermolysin with increasing pressure. Thermal stability, however, was affected very little by complex formation with SMPI. Phosphoramidon, Cbz-Phe-Gly-NH2 and Cbz-Phe also positively affected the pressure-tolerance of thermolysin, in the following order: Cbz-Gly-Phe-NH2 < Cbz-Phe < phosphoramidon. The third compound exhibited stabilizing effects comparable with those of SMPI, which suggests that the interaction between SMPI and thermolysin was localized to the reactive site. 相似文献
5.
Madhusoodana P. Nambiar Tatsuya Oda Chaohua Chen Yasuo Kuwazuru Henry C. Wu 《Journal of cellular physiology》1993,154(2):222-228
The intracellular pathway following receptor-mediated endocytosis of cholera toxin was studied using brefeldin A (BFA), which inhibited protein secretion and induced dramatic morphological changes in the Golgi region. In both mouse Y1 adrenal cells and CHO cells, BFA at 1 μg/ml caused a 80–90% inhibition of the cholera toxin (CT)-elevation of intracellular cAMP. The inhibition of the cytotoxicity of CT by BFA was also observed in a rounding assay of Y1 adrenal cells. The inhibition of CT cytotoxicity by BFA was dose dependent, with the ID50 value similar to the LD50 of BFA in Y1 adrenal cells. Binding and internalization of [125I]-cholera toxin in Y1 adrenal cells was not affected by BFA. Unlike the BFA-sensitive cell lines such as Y1 adrenal and CHO cells, BFA at 1 μg/ml did not inhibit the cytotoxicity of CT in PtK1 cells, of which the Golgi structure was BFA-resistant. These results strongly suggest that a BFA-sensitive Golgi is required for the protection of CT cytotoxicity by BFA. In contrast, elevation of the intracellular cAMP by forskolin, which acts directly on the plasma membrane adenylate cyclase, was not affected by BFA. These observations indicate that the intoxication of target cells by CT requires an intact Golgi region for its intracellular trafficking and/or processing. In this respect, CT shares a common intracellular pathway with ricin, Pseudomonas toxin, and modeccin, even though their structures and modes of action are very different. © 1993 Wiley-Liss, Inc. 相似文献
6.
Toshifumi Nakao Ichiro Yamato Yasuhiro Anraku 《Molecular & general genetics : MGG》1987,208(1-2):70-75
7.
Identification of I:A mismatch base-pairing structure in DNA 总被引:7,自引:0,他引:7
S Uesugi Y Oda M Ikehara Y Kawase E Ohtsuka 《The Journal of biological chemistry》1987,262(15):6965-6968
Deoxyoligonucleotides containing deoxyinosine residues at positions corresponding to ambiguous nucleotides derived from an amino acid sequence have been successfully used as hybridization probes. It is assumed that the hypoxanthine residue can make base pairs with multiple bases. In order to obtain direct evidence for I:A base-pairing, a self-complementary deoxyoligonucleotide, d(G-G-I-A-C-C), was synthesized and its properties were examined by NMR spectroscopy. Three hydrogen-bonded imino proton resonances are observed at low temperatures in H2O suggesting the formation of a self-duplex with complete base pairing. Nuclear Overhauser effect (NOE) experiments showed that a signal at 15.1 ppm originated from the imino proton (H1) of the dI residue (I3) which is hydrogen-bonded to the dA residue (A4). Both the I3 and A4 residues were assumed to have taken an anti glycosidic conformation since irradiating the H1 of I3 gave NOEs both to its own H2 and to that of A4, an NOE also being observed between the H2 protons of I3 and A4. Comparison of the 31P NMR spectra of d(G-G-I-A-C-C) and d(G-G-I-C-C-C) showed the backbone structure of d(G-G-I-A-C-C) to have been disturbed by the presence of purine:purine base pairs in the middle of the hexamer duplex. 相似文献
8.
For construction of bifunctionally active membrane-bound fusion proteins, we designed plasmids encoding fusion proteins in which the carboxyl terminus of Escherichia coli proline carrier was joined to the amino terminus of E. coli beta-galactosidase directly or with a collagen linker inserted between the two. The expressions of these fusion proteins complemented deficiencies in both proline transport and beta-galactosidase activity in E. coli cells. The fusion proteins were stable and mostly localized in the cytoplasmic membrane. The proline transport activities of the fusion proteins were kinetically similar to that of the wild type proline carrier. The beta-galactosidase moiety of the collagen-linked fusion protein was liberated from membrane vesicles by collagenase treatment. The Km value of released beta-galactosidase for o-nitrophenyl beta-D-galactopyranoside hydrolysis was similar to that of membrane-bound beta-galactosidase in the fusion protein. These results indicated that the fusion proteins are bifunctionally active and exhibit normal proline transport and beta-galactosidase activities. The crypticity of the beta-galactosidase activity associated with the fusion proteins indicated that the carboxyl terminus of the proline carrier was located on the cytoplasmic side of the membrane. 相似文献
9.
Extracellular serratial protease (56,000 Da) is known to be cytotoxic. Fluorescein isothiocyanate-labeled protease was found to form a complex with human alpha 2-macroglobulin (alpha 2M), and this enzyme-inhibitor complex was purified. The protease was found to be internalized by fibroblasts in culture as a complex with alpha 2M, which resulted in cell destruction. Regeneration of enzyme activity was confirmed in cells after 2-3 h of incubation. Chicken egg-white ovomacroglobulin, a homolog of human alpha 2M, formed a complex with this enzyme similarly and more tightly but failed to exhibit protease activity, cytotoxicity, and internalization into cells. 相似文献
10.
A mixture of extracellular carrageenases was isolated from the cell-free medium of a culture of marine Cytophaga sp. 1k-C783 grown on ZoBell 2216 E broth with 0.1% commercial carrageenan. A single active peak of kappa-carrageenase was separated and purified from the mixture by ammonium sulfate precipitation, ion-exchange chromatography, and Sephadex G-200 gel filtration chromatography. Molecular weight of the purified kappa-carrageenase was estimated as 100,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified kappa-carrageenase had pH optimum 7.6 and temperature optimum 25 C. 相似文献