全文获取类型
收费全文 | 17305篇 |
免费 | 43篇 |
国内免费 | 54篇 |
专业分类
系统科学 | 254篇 |
丛书文集 | 444篇 |
教育与普及 | 36篇 |
理论与方法论 | 50篇 |
现状及发展 | 7975篇 |
研究方法 | 732篇 |
综合类 | 7762篇 |
自然研究 | 149篇 |
出版年
2012年 | 206篇 |
2011年 | 419篇 |
2010年 | 99篇 |
2009年 | 94篇 |
2008年 | 275篇 |
2007年 | 348篇 |
2006年 | 295篇 |
2005年 | 304篇 |
2004年 | 275篇 |
2003年 | 330篇 |
2002年 | 265篇 |
2001年 | 611篇 |
2000年 | 612篇 |
1999年 | 344篇 |
1992年 | 329篇 |
1991年 | 253篇 |
1990年 | 298篇 |
1989年 | 271篇 |
1988年 | 262篇 |
1987年 | 277篇 |
1986年 | 284篇 |
1985年 | 338篇 |
1984年 | 242篇 |
1983年 | 220篇 |
1982年 | 202篇 |
1981年 | 238篇 |
1980年 | 261篇 |
1979年 | 568篇 |
1978年 | 463篇 |
1977年 | 469篇 |
1976年 | 351篇 |
1975年 | 374篇 |
1974年 | 583篇 |
1973年 | 455篇 |
1972年 | 416篇 |
1971年 | 510篇 |
1970年 | 656篇 |
1969年 | 573篇 |
1968年 | 493篇 |
1967年 | 531篇 |
1966年 | 440篇 |
1965年 | 332篇 |
1964年 | 86篇 |
1959年 | 198篇 |
1958年 | 293篇 |
1957年 | 192篇 |
1956年 | 172篇 |
1955年 | 167篇 |
1954年 | 159篇 |
1948年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
Wolfs JL Comfurius P Bekers O Zwaal RF Balasubramanian K Schroit AJ Lindhout T Bevers EM 《Cellular and molecular life sciences : CMLS》2009,66(2):314-323
The exposure of phosphatidylserine (PS) at the cell surface plays a critical role in blood coagulation and serves as a macrophage
recognition moiety for the engulfment of apoptotic cells. Previous observations have shown that a high extracellular [K+] and selective K+ channel blockers inhibit PS exposure in platelets and erythrocytes. Here we show that the rate of PS exposure in erythrocytes
decreases by ~50% when the intracellular [K+] increases from 0 to physiological concentrations. Using resealed erythrocyte membranes, we further show that lipid scrambling
is inducible by raising the intracellular [Ca2+] and that K+ ions have a direct inhibitory effect on this process. Lipid scrambling in resealed ghosts occurs in the absence of cell shrinkage
and microvesicle formation, processes that are generally attributed to Ca2+-induced lipid scrambling in intact erythrocytes. Thus, opening of Ca2+-sensitive K+ channels causes loss of intracellular K+ that results in reduced intrinsic inhibitory effect of these ions on scramblase activity.
Received 11 September 2008; received after revision 17 October 2008; accepted 27 October 2008 相似文献
262.
G. M. C. Janssen P. Schwertman T. A. T. Wanga R. S. Jahangir Tafrechi P. J. A. van den Broek A. K. Raap 《Cellular and molecular life sciences : CMLS》2009,66(4):721-730
Cytoplasmic translation is under sophisticated control but how cells adapt its rate to constitutive loss of mitochondrial
oxidative phosphorylation is unknown. Here we show that translation is repressed in cells with the pathogenic A3243G mtDNA
mutation or in mtDNA-less ρ0 cells by at least two distinct pathways, one transiently targeting elongation factor eEF-2 and the other initiation factor
eIF-2α constitutively. Under conditions of exponential cell growth and mammalian target of rapamycin (mTOR) activation, eEF-2
becomes transiently phosphorylated by an AMP-activated protein kinase (AMPK)-dependent pathway, especially high in mutant
cells. Independent of AMPK and mTOR, eIF-2α is constitutively phosphorylated in mutant cells, likely a signature of endoplasmic
reticulum (ER)-stress response induced by the loss of oxidative phosphorylation. While the AMPK/eEF-2K/eEF-2 pathway appears
to function in adaptation to physiological fluctuations in ATP levels in the mutant cells, the ER stress signified by constitutive
protein synthesis inhibition through eIF-2α-mediated repression of translation initiation may have pathobiochemical consequences.
Received 29 October 2008; received after revision 11 December 2008; accepted 16 December 2008 相似文献
263.
A. Shukla P. Chaurasia S. R. Bhaumik 《Cellular and molecular life sciences : CMLS》2009,66(8):1419-1433
Methylation of lysine residues of histones is associated with functionally distinct regions of chromatin, and, therefore,
is an important epigenetic mark. Over the past few years, several enzymes that catalyze this covalent modification on different
lysine residues of histones have been discovered. Intriguingly, histone lysine methylation has also been shown to be cross-regulated
by histone ubiquitination or the enzymes that catalyze this modification. These covalent modifications and their cross-talks
play important roles in regulation of gene expression, heterochromatin formation, genome stability, and cancer. Thus, there
has been a very rapid progress within past several years towards elucidating the molecular basis of histone lysine methylation
and ubiquitination, and their aberrations in human diseases. Here, we discuss these covalent modifications with their cross-regulation
and roles in controlling gene expression and stability.
Received 24 September 2008; received after revision 21 November 2008; accepted 28 November 2008 相似文献
264.
265.
266.
267.
268.
269.
Huet J Wyckmans J Wintjens R Boussard P Raussens V Vandenbussche G Ruysschaert JM Azarkan M Looze Y 《Cellular and molecular life sciences : CMLS》2006,63(24):3042-3054
Two chitinases, able to use tetra-N-acetylglucosamine, chitin and chitosan as substrates, were characterized after purification from Carica papaya latex. The complete amino acid sequence of the major form and about 40% of the minor one were determined through proteolytic
digestions and mass spectroscopy analysis. Sequencing demonstrated that both papaya chitinases are members of the family 19
of glycosyl hydrolases (GH19). Based on the known 3-D structures of other members of family GH19, it was expected that papaya
chitinases would adopt all-alpha structures. However, circular dichroism and infrared spectroscopy indicated, for the papaya
chitinases, a content of 15–20% of extended structures besides the expected 40% of alpha helices. Since the fully sequenced
papaya chitinase contains a large number of proline residues the possibility that papaya chitinase contains polyproline II
stretches was examined in the context of their resistance against proteolytic degradation.
Received 11 July 2006; received after revision 13 October 2006; accepted 25 October 2006 相似文献
270.
Kramer J Böhrnsen F Lindner U Behrens P Schlenke P Rohwedel J 《Cellular and molecular life sciences : CMLS》2006,63(5):616-626
Microfracture of subchondral bone results in intrinsic repair of cartilage defects. Stem or progenitor cells from bone marrow
have been proposed to be involved in this regenerative process. Here, we demonstrate for the first time that mesenchymal stem
(MS) cells can in fact be recovered from matrix material saturated with cells from bone marrow after microfracture. This also
introduces a new technique for MS cell isolation during arthroscopic treatment. MS cells were phenotyped using specific cell
surface antibodies. Differentiation of the MS cells into the adipogenic, chondrogenic and osteogenic lineage could be demonstrated
by cultivation of MS cells as a monolayer, as micromass bodies or mesenchymal microspheres. This study demonstrates that MS
cells can be attracted to a cartilage defect by guidance of a collagenous matrix after perforating subchondral bone. Protocols
for application of MS cells in restoration of cartilage tissue include an initial invasive biopsy to obtain the MS cells and
time-wasting in vitro proliferation and possibly differentiation of the cells before implantation. The new technique already includes attraction
of MS cells to sites of cartilage defects and therefore may overcome the necessity of in vitro proliferation and differentiation of MS cells prior to transplantation.
Received 3 November 2005; received after revision 15 December 2005; accepted 4 January 2006 相似文献