全文获取类型
收费全文 | 21230篇 |
免费 | 464篇 |
国内免费 | 885篇 |
专业分类
22579篇 |
出版年
2023年 | 105篇 |
2022年 | 171篇 |
2021年 | 221篇 |
2020年 | 190篇 |
2019年 | 257篇 |
2018年 | 303篇 |
2017年 | 236篇 |
2016年 | 266篇 |
2015年 | 582篇 |
2014年 | 1648篇 |
2013年 | 1651篇 |
2012年 | 1624篇 |
2011年 | 2289篇 |
2010年 | 2015篇 |
2009年 | 984篇 |
2008年 | 955篇 |
2007年 | 871篇 |
2006年 | 810篇 |
2005年 | 708篇 |
2004年 | 657篇 |
2003年 | 617篇 |
2002年 | 432篇 |
2001年 | 260篇 |
2000年 | 281篇 |
1999年 | 296篇 |
1998年 | 316篇 |
1997年 | 292篇 |
1996年 | 281篇 |
1995年 | 323篇 |
1994年 | 297篇 |
1993年 | 239篇 |
1992年 | 209篇 |
1991年 | 200篇 |
1990年 | 183篇 |
1989年 | 175篇 |
1988年 | 141篇 |
1987年 | 140篇 |
1986年 | 111篇 |
1985年 | 177篇 |
1984年 | 233篇 |
1983年 | 179篇 |
1982年 | 172篇 |
1981年 | 99篇 |
1980年 | 127篇 |
1979年 | 92篇 |
1978年 | 42篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1974年 | 15篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Reconstituted Na+,K+-ATPase from either pig kidney or shark rectal glands was phosphorylated by cAMP dependent protein kinase, PKA. The stoichiometry was 0.9 mole Pi/mole -subunit in the pig kidney enzyme and 0.2 mol Pi/mol -subunit in the shark enzyme. In shark Na+,K+-ATPase PKA phosphorylation increased the maximum hydrolytic activity for cytoplasmic Na+ activation and extracellular K+ activation without affecting the apparent Km values. In contrast, no significant functional effect after PKA phosphorylation was observed in pig kidney Na+,K+-ATPase. 相似文献
122.
Protein Kinases Are Involved in Prolonged Acetylcholine Release from Rat Hippocampus Induced by Thyrotropin-Releasing Hormone Analogue NS-3 总被引:2,自引:0,他引:2
Michiko Oka Yoshinori Itoh Yojiro Ukai Yoshiaki Yoshikuni Kiyoshi Kimura 《Journal of neurochemistry》1996,66(5):1889-1893
Abstract: The effects of various protein kinase inhibitors on acetylcholine release from the rat hippocampus induced by the local application of NS-3 (montirelin hydrate, CG-3703), a thyrotropin-releasing hormone analogue, into the medial septum-diagonal band were examined using in vivo microdialysis. Perfusion of NS-3 (1 µ M ) into the medial septum-diagonal band for 20 min produced a pronounced and prolonged increase in the hippocampal acetylcholine efflux. Pretreatment of the medial septum-diagonal band with either K-252a, a nonselective protein kinase inhibitor, or selective protein kinase A inhibitor H-89 almost completely blocked the acetylcholine efflux evoked by NS-3, and selective protein kinase C inhibitor calphostin C inhibited the action of NS-3. On the other hand, NS-3 (0.1–10 µ M ) or TRH (1–100 µ M ) increased the cyclic AMP efflux from the medial septum-diagonal band in a concentration-dependent manner, as measured by microdialysis. These findings suggest that protein kinases A and C in the neurons of the medial septum-diagonal band are involved in the mechanism of the prolonged stimulation of acetylcholine release from the hippocampus induced by thyrotropin-releasing hormone and its analogue, NS-3. 相似文献
123.
L. Zavalova S. Lukyanov I. Baskova E. Snezhkov S. Akopov S. Berezhnoy E. Bogdanova E. Barsova E. D. Sverdlov 《Molecular & general genetics : MGG》1996,253(1-2):20-25
We previously detected in salivary gland secretions of the medicinal leech (Hirudo medicinalis) a novel enzymatic activity, endo-ɛ(γ-Glu)-Lys isopeptidase, which cleaves isopeptide bonds formed by transglutaminase (Factor
XIIIa) between glutamine γ-carboxamide and the ɛ-amino group of lysine. Such isopeptide bonds, either within or between protein
polypeptide chains are formed in many biological processes. However, before we started our work no enzymes were known to be
capable of specifically splitting isopeptide bonds in proteins. The isopeptidase activity we detected was specific for isopeptide
bonds. The enzyme was termed destabilase. Here we report the first purification of destabilase, part of its amino acid sequence,
isolation and sequencing of two related cDNAs derived from the gene family that encodes destabilase proteins, and the detection
of isopeptidase activity encoded by one of these cDNAs cloned in a baculovirus expression vector. The deduced mature protein
products of these cDNAs contain 115 and 116 amino acid residues, including 14 highly conserved Cys residues, and are formed
from precursors containing specific leader peptides. No homologous sequences were found in public databases.
Received: 9 April 1996 / Accepted: 17 May 1996 相似文献
124.
Birgit Conrad Regina S. Savchenko Roland Breves Jürgen Hofemeister 《Molecular & general genetics : MGG》1996,250(2):230-236
The adaptation and application of theEscherichia coli T7 RNA polymerase system for regulated and promoter-specific gene expression inBacillus subtilis is reported. The expression cassette used inBacillus subtilis was tightly regulated and T7 RNA polymerase (T7 RNAP) appeared 30 min after induction. The efficiency of T7 promoter-specific gene expression inB. subtilis was studied using one secretory and two cytosolic proteins of heterologous origin. The accumulation ofE. coli -galactosidase, as well as a 1,4--glucosidase fromThermoanaerobacter brockii inB. subtilis after T7 RNAP induction was strongly enhanced by rifampicin inhibition of host RNAP activity. The-amylase ofThermoactinomyces vulgaris, a secretory protein, was found to accumulate in the culture supernatant up to levels of about 70 mg/l 10–20 h after T7 RNAP induction, but was also deposited in cellular fractions. The addition of rifampicin inhibited-amylase secretion, but unexpectedly, after a short period, also prevented its further (intra)cellular accumulation 相似文献
125.
The MC dynamics of an off-lattice all-atom protein backbone model with rigid amide planes are studied. The only degrees of freedom are the dihedral angle pairs of the C-atoms. Conformational changes are generated by Monte Carlo (MC) moves. The MC moves considered are single rotations (simple moves, SM's) giving rise to global conformational changes or, alternatively, cooperative rotations in a window of amide planes (window moves, WM's) generating local conformational changes in the window. Outside the window the protein conformation is kept invariant by constraints. These constraints produce a bias in the distribution of dihedral angles. The WM's are corrected for this bias by suitable Jacobians. The energy function used is derived from the CHARMM force field. In a first application to polyalanine it is demonstrated that WM's sample the conformational space more efficiently than SM's.Abbreviations CPU
Central Processing Unit
- MC
Monte Carlo
- MCD
Monte Carlo Dynamics
- MD
Molecular Dynamics
- RMS
Root-Mean-Square
- RMSD
Root-Mean-Square-Deviation
- SM
Simple Move
- WM
Window Move 相似文献
126.
Trypsin-subtilisin inhibitor from marine turtle eggwhite refolded quantitatively from its fully reduced state atpH 8.5 in the presence of reduced and oxidized glutathione. The refolding process was studied by following the accompanying changes in inhibitory activity, fluorescence, sulfhydryl group titer, and hydrodynamic volume. The refolding process followed second-order kinetics with rate constants of 4.80×102 M–1 sec–1 for trypsin-inhibiting domain and 0.77× 102 M–1 sec–1 for subtilisin-inhibiting domain of the inhibitor at 30°C and their respective activation energies of the refolding process were 15.9 and 21.6 kcal/mol. Fluorescence intensity of the reduced inhibitor decreased with time of refolding until it corresponded to the intensity of the native inhibitor. The inhibitor contained 1–2%-helix, 40–42%-sheet, and 57–58% random coil structure. Refolded inhibitor gave a circular dichroic spectrum identical to that of the native inhibitor. A number of principal intermediates were detected as a function of the refolding time. Size-exclusion chromatography separated the intermediates differing in hydrodynamic volume (Stokes radius). The Stokes radius ranged from 23 Å (fully reduced inhibitor) to 18.8 Å (native inhibitor). Results indicated the independent refolding of two domains of the inhibitor and multiple pathways of folding were followed rather than an ordered sequential pathway. 相似文献
127.
Jonathan A. Lindquist Elisabeth Barofsky Philip N. McFadden 《Journal of Protein Chemistry》1996,15(1):115-122
Protein (d-aspartyl/l-isoaspartyl) carboxyl methyltransferase (PCM, E.C. 2.1.1.77) was previously shown to be enzymatically methyl esterified in an autocatalytic manner at altered aspartyl residues; methyl esters are observed in a subpopulation of the enzyme termed thePCM fraction [Lindquist and McFadden (1994),J. Protein Chem.
13, 23–30]. The altered aspartyl sites serving as methyl acceptors inPCM have now been localized by using proteolytic enzymes and chemical cleavage techniques in combination with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to identify fragments of the [3H]automethylated enzyme that contain a [3H]methyl ester. Methylation was positively identified at positions Asn188 and Asp217 in the enzyme sequence, a consequence of the spontaneous alteration of these sites tol-isoaspartyl ord-aspartyl sites and their methylation by active PCM molecules. The identification of more than one site of automethylation shows thatPCM is not a homogeneous population of damaged PCM molecules, but rather a complex population of molecules with a variety of age-altered damage sites.Abbreviations PCM
protein (d-aspartyl/l-isoaspartyl) carboxyl methyltransferase
- EDTA
disodium ethylenediaminetetraacetate
- PMSF
phenylmethylsulfonyl fluoride
- TEA
trifluoroacetic acid
- HPLC
high-pressure liquid chromatography 相似文献
128.
The lactose permease is being used as a model system for the rational redesign of a membrane protein with the goal of increasing the likelihood of crystallization. Various modifications to the protein have been added for the purposes of purification, stability, and potential for crystallization. The addition of six consecutive histidines at the C-terminus of the protein allows for the rapid purification by nickel-chelate chromatography, and the insertion of an entire protein domain into one of the inner cytoplasmic loops of the permease gives the resulting protein a larger hydrophilic surface area. The increase in polar surface area makes the fusion protein easier to handle and more likely to crystallize. In particular, the introduction of cytochromeb562 ofE. coli into the central hydrophilic domain of the lac permease results in a fusion protein with the transport activity of the permease and the visible absorbance spectrum of the cytochrome. The red permease is very easy to monitor through the steps of expression, purification, concentration, and crystallization. 相似文献
129.
C. Rabarivola B. Meier C. Langer W. Scheffrahn Y. Rumpler 《Primates; journal of primatology》1996,37(2):215-225
Analysis for genetic variation of insular and mainland populations ofEulemur macaco has revealed: (1) a different degree of genetic variation between populations; and (2) the phylogenetic relationships between
groups, on the islands of Nosy-Be and Nosy-Komba, and in the Peninsula of Ambato (Madagascar). Eleven systems of blood proteins
from 157 animals were used as genetic markers. The genetic variation was lower on the island of Nosy-Komba than in the mainland
of Ambato. This is consistent with the expectation that genetic variation is lower on islands than on mainlands. In contrast,
the genetic variation on the island of Nosy-Be was the highest of the three populations. This finding can best be explained
by assuming that the sample of Nosy-Be consists of individuals of several small isolated groups, where genetic drift computation
showed the population of Nosy-Be to be distinct, and the populations of Nosy-Komba and Ambato to be close within the same
branch of the dendrogram. These findings give an insight into the population history of the island of Nosy-Komba, which might
have been populated by mainland groups from Ambato. 相似文献
130.
Characterization of a calcium/calmodulin-dependent protein kinase homolog from maize roots showing light-regulated gravitropism 总被引:14,自引:0,他引:14
Roots of many species respond to gravity (gravitropism) and grow downward only if illuminated. This light-regulated root gravitropism is phytochrome-dependent, mediated by calcium, and inhibited by KN-93, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaMK II). A cDNA encoding MCK1, a maize homolog of mammalian CaMK, has been isolated from roots of maize (Zea mays L.). The MCK1 gene is expressed in root tips, the site of perception for both light and gravity. Using the [35S]CaM gel-overlay assay we showed that calmodulin-binding activity of the MCK1 is abolished by 50 M KN-93, but binding is not affected by 5 M KN-93, paralleling physiological findings that light-regulated root gravitropism is inhibited by 50 M KN-93, but not by 5 M KN-93. KN-93 inhibits light-regulated gravitropism by interrupting transduction of the light signal, not light perception, suggesting that MCK1 may play a role in transducing light. This is the first report suggesting a physiological function for a CaMK homolog in light signal transduction.Abbreviations CaM
calmodulin
- CaMK (II)
Ca2+/calmodulin-dependent protein kinase (II)
- CBP
CaM-binding protein
- CDPK
Ca2+-dependent protein kinase
- MCK1
maize homolog of mamalian CaMK
This work is supported by the National Aeronautics and Space Administration grant No: NAGW 238. 相似文献