全文获取类型
收费全文 | 2361篇 |
免费 | 273篇 |
国内免费 | 32篇 |
出版年
2021年 | 23篇 |
2020年 | 26篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 35篇 |
2015年 | 56篇 |
2014年 | 61篇 |
2013年 | 86篇 |
2012年 | 104篇 |
2011年 | 100篇 |
2010年 | 69篇 |
2009年 | 55篇 |
2008年 | 68篇 |
2007年 | 96篇 |
2006年 | 82篇 |
2005年 | 81篇 |
2004年 | 100篇 |
2003年 | 93篇 |
2002年 | 88篇 |
2001年 | 79篇 |
2000年 | 93篇 |
1999年 | 72篇 |
1998年 | 29篇 |
1997年 | 31篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 53篇 |
1991年 | 63篇 |
1990年 | 58篇 |
1989年 | 57篇 |
1988年 | 54篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 32篇 |
1984年 | 23篇 |
1983年 | 33篇 |
1982年 | 26篇 |
1981年 | 23篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1977年 | 23篇 |
1975年 | 27篇 |
1974年 | 26篇 |
1973年 | 31篇 |
1972年 | 21篇 |
1971年 | 24篇 |
1970年 | 22篇 |
排序方式: 共有2666条查询结果,搜索用时 46 毫秒
71.
Enhancement of selectivity in recognition of nucleic acids via chemical autoligation. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A new approach to increase the selectivity of interaction between oligonucleotide probes and target nucleic acids is described. In place of a single, relatively long oligonucleotide probe, two or three short oligomers terminated by thiophosphoryl and bromoacetamido groups are employed. Fast and efficient autoligation takes place when the oligomers hybridize in a contiguous mode to the same complementary strand such that a thiophosphoryl group on one strand and a bromoacetamido group on another are brought into proximity. A single nucleotide mismatch for the short probes leads to marked reduction in the rate of autoligation. The binding affinity of the product is close to that for a natural probe of the same length. This approach could have potential in oligonucleotide-based diagnostics, chemical amplification systems, and therapeutic applications. 相似文献
72.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
73.
C. David Pauza Peter Emau Maria S. Salvato Parul Trivedi Debra MacKenzie Miroslav Malkovsky Hideo Uno Kevin T. Schultz 《Journal of medical primatology》1993,22(2-3):154-161
Intrarectal inoculation of rhesus monkeys with low doses of SIVmac led to a prolonged clinical and virological latency that was not observed for high intrarectal doses or for intravenous inoculation. Animals infected intrarectally with low virus doses remained negative for serum antibody responses to SIV for at least one year even though they readily transferred SIV to naive recipients via transfusion of whole blood. 相似文献
74.
75.
76.
77.
Alfonso Gonzalez Terry D. Oberley Janice L. Schultz Jennifer Ostrom Jonathan J. Li 《In vitro cellular & developmental biology. Animal》1993,29(7):562-573
Summary Primary diethylstilbestrol-induced kidney tumors from Syrian hamsters were grown in vitro and maintained in culture for 6
mo. Combined immunohistochemical studies using antibodies to intermediate filaments and ultrastructural studies of tumor cells
in culture exhibited characteristics similar to tumor cells in vivo. Furthermore, the cells manifested transformed properties
in culture; they grew both as multilayered colonies attached to the tissue culture substrate and as floating multicellular
colonies (spheroids). When cultured cells were injected into diethylstilbestrol-treated recipient hamsters, tumors developed
at the injection sites. In contrast, renal tubules or whole kidney cortex from control hamsters cultured in the same medium
underwent only short-term growth, with senescence developing after approximately 1 mo. However, cell cultures of kidney cortex
from animals treated in vivo for 5 mo. with diethylstilbestrol formed a cell line. This diethylstilbestrol-induced cell line
has been maintained in culture for 1.5 yr and has the following characteristics: a) it is anchorage-dependent, b) it is negative
in in vivo tumorigenicity tests, and c) cultured cells are histochemically and ultrastructurally similar to cultured tumor
cells. This culture system should prove to be of use in studying hormonal carcinogenesis in vitro.
This study was supported by the Medical Research Service, Department of Veterans Affairs, Washington, DC, and by grant CA-22008
from the National Cancer Institute, NIH, DHHS, Bethesda, MD. 相似文献
78.
The Metabolism of Quinate in Pea Roots (Purification and Partial Characterization of a Quinate Hydrolyase) 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A quinate (QA) hydrolyase was isolated from pea (Pisum sativum L.) roots. The enzyme converts QA into shikimate by elimination of water. The enzymatic reaction is independent of cofactors and divalent cations. The QA hydrolyase was purified about 1,600-fold to apparent electrophoretic homogeneity in three steps, including bovine serum albumin-affinity chromatography. The enzyme forms oligomers and/or complexes with bovine serum albumin and ovalbumin. The monomer molecular weight of the enzyme is about 15,000. The hydrolyase shows regular Michaelis-Menten kinetics with a Km, of 2.0 mM for QA. Compartmentation studies reveal that the QA hydrolyase is localized in plastids. The QA hydrolyase may function in channeling imported QA into the shikimate pathway to support aromatic amino acid biosynthesis in plastids. 相似文献
79.
Mammalian DNA ligase III: molecular cloning, chromosomal localization, and expression in spermatocytes undergoing meiotic recombination. 总被引:14,自引:4,他引:10
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
80.
Expression of TRPC3 in Chinese Hamster Ovary Cells Results in Calcium-activated Cation Currents Not Related to Store Depletion 总被引:16,自引:0,他引:16
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Christof Zitt Alexander G. Obukhov Carsten Strübing Andrea Zobel Frank Kalkbrenner Andreas Lückhoff Günter Schultz 《The Journal of cell biology》1997,138(6):1333-1341
TRPC3 (or Htrp3) is a human member of the trp family of Ca2+-permeable cation channels. Since expression of TRPC3 cDNA results in markedly enhanced Ca2+ influx in response to stimulation of membrane receptors linked to phospholipase C (Zhu, X., J. Meisheng, M. Peyton, G. Bouley, R. Hurst, E. Stefani, and L. Birnbaumer. 1996. Cell. 85:661–671), we tested whether TRPC3 might represent a Ca2+ entry pathway activated as a consequence of depletion of intracellular calcium stores. CHO cells expressing TRPC3 after intranuclear injection of cDNA coding for TRPC3 were identified by fluorescence from green fluorescent protein. Expression of TRPC3 produced cation currents with little selectivity for Ca2+ over Na+. These currents were constitutively active, not enhanced by depletion of calcium stores with inositol-1,4,5-trisphosphate or thapsigargin, and attenuated by strong intracellular Ca2+ buffering. Ionomycin led to profound increases of currents, but this effect was strictly dependent on the presence of extracellular Ca2+. Likewise, infusion of Ca2+ into cell through the patch pipette increased TRPC3 currents. Therefore, TRPC3 is stimulated by a Ca2+-dependent mechanism. Studies on TRPC3 in inside-out patches showed cation-selective channels with 60-pS conductance and short (<2 ms) mean open times. Application of ionomycin to cells increased channel activity in cell-attached patches. Increasing the Ca2+ concentration on the cytosolic side of inside-out patches (from 0 to 1 and 30 μM), however, failed to stimulate channel activity, even in the presence of calmodulin (0.2 μM). We conclude that TRPC3 codes for a Ca2+-permeable channel that supports Ca2+-induced Ca2+-entry but should not be considered store operated. 相似文献