全文获取类型
收费全文 | 19452篇 |
免费 | 109篇 |
国内免费 | 228篇 |
专业分类
系统科学 | 422篇 |
丛书文集 | 382篇 |
教育与普及 | 72篇 |
理论与方法论 | 78篇 |
现状及发展 | 7252篇 |
研究方法 | 829篇 |
综合类 | 10170篇 |
自然研究 | 584篇 |
出版年
2014年 | 152篇 |
2013年 | 299篇 |
2012年 | 520篇 |
2011年 | 1073篇 |
2010年 | 378篇 |
2009年 | 357篇 |
2008年 | 560篇 |
2007年 | 640篇 |
2006年 | 647篇 |
2005年 | 581篇 |
2004年 | 427篇 |
2003年 | 341篇 |
2002年 | 347篇 |
2001年 | 526篇 |
2000年 | 571篇 |
1999年 | 422篇 |
1992年 | 304篇 |
1991年 | 262篇 |
1990年 | 257篇 |
1989年 | 234篇 |
1988年 | 211篇 |
1987年 | 235篇 |
1986年 | 211篇 |
1985年 | 257篇 |
1984年 | 255篇 |
1983年 | 171篇 |
1982年 | 187篇 |
1981年 | 174篇 |
1980年 | 207篇 |
1979年 | 475篇 |
1978年 | 368篇 |
1977年 | 400篇 |
1976年 | 298篇 |
1975年 | 349篇 |
1974年 | 475篇 |
1973年 | 421篇 |
1972年 | 393篇 |
1971年 | 459篇 |
1970年 | 538篇 |
1969年 | 469篇 |
1968年 | 478篇 |
1967年 | 488篇 |
1966年 | 421篇 |
1965年 | 337篇 |
1964年 | 146篇 |
1959年 | 169篇 |
1958年 | 241篇 |
1957年 | 191篇 |
1956年 | 147篇 |
1955年 | 159篇 |
排序方式: 共有10000条查询结果,搜索用时 672 毫秒
391.
Many notions regarding the function, structure and regulation of cholera toxin expression have remained essentially unaltered
in the last 15 years. At the same time, recent findings have generated additional perspectives. For example, the cholera toxin
genes are now known to be carried by a non-lytic bacteriophage, a previously unsuspected condition. Understanding of how the
expression of cholera toxin genes is controlled by the bacterium at the molecular level has advanced significantly and relationships
with cell-density-associated (quorum-sensing) responses have recently been discovered. Regarding the cell intoxication process,
the mode of entry and intracellular transport of cholera toxin are becoming clearer. In the immunological field, the strong
oral immunogenicity of the non-toxic B subunit of cholera toxin (CTB) has been exploited in the development of a now widely
licensed oral cholera vaccine. Additionally, CTB has been shown to induce tolerance against co-administered (linked) foreign
antigens in some autoimmune and allergic diseases.
Received 25 October 2007; accepted 12 December 2007 相似文献
392.
Molecular and Cellular Basis of Regeneration and Tissue Repair 总被引:3,自引:0,他引:3
Rossi L Salvetti A Batistoni R Deri P Gremigni V 《Cellular and molecular life sciences : CMLS》2008,65(1):16-23
Planarians possess amazing abilities to regulate tissue homeostasis and regenerate missing body parts. These features reside on the presence of a population of pluripotent/totipotent stem cells, the neoblasts, which are considered as the only planarian cells able to proliferate in the asexual strains. Neoblast distribution has been identified by mapping the cells incorporating bromodeoxyuridine, analyzing mitotic figures and using cell proliferation markers. Recently identified molecular markers specifically label subgroups of neoblasts, revealing thus the heterogeneity of the planarian stem cell population. Therefore, the apparent totipotency of neoblasts probably reflects the composite activities of multiple stem cell types. First steps have been undertaken to understand how neoblasts and differentiated cells communicate with each other to adapt the self-renewal and differentiation rates of neoblasts to the demands of the body. Moreover, the introduction of molecular resource database on planarians now paves the way to renewed strategies to understand planarian regeneration and stem cell-related issues. 相似文献
393.
Dolezel D Zdechovanova L Sauman I Hodkova M 《Cellular and molecular life sciences : CMLS》2008,65(6):964-969
Current models state that insect peripheral oscillators are directly responsive to light, while mammalian peripheral clock
genes are coordinated by a master clock in the brain via intermediate factors, possibly hormonal. We show that the expression
levels of two circadian clock genes, period (per) and Par Domain Protein 1 (Pdp1) in the peripheral tissue of an insect model species, the linden bug Pyrrhocoris apterus, are inversely affected by contrasting photoperiods. The effect of photoperiod on per and Pdp1 mRNA levels was found to be mediated by the corpus allatum, an endocrine gland producing juvenile hormone. Our results
provide the first experimental evidence for the effect of an endocrine gland on circadian clock gene expression in insects.
Received 31 October 2007; received after revision 7 January 2008; accepted 9 January 2008
D. Dolezel, L. Zdechovanova: These authors contributed equally to this work. 相似文献
394.
Bile acids and bile alcohols in the form of their conjugates are amphipathic end products of cholesterol metabolism with multiple physiological functions. The great variety of bile acids and bile alcohols that are present in vertebrates are tabulated. Bile salts have an enterohepatic circulation resulting from efficient vectorial transport of bile salts through the hepatocyte and the ileal enterocyte; such transport leads to the accumulation of a pool of bile salts that cycles between the liver and intestine. Bile salt anions promote lipid absorption, enhance tryptic cleavage of dietary proteins, and have antimicrobial effects. Bile salts are signaling molecules, activating nuclear receptors in the hepatocyte and ileal enterocyte, as well as an increasing number of G-protein coupled receptors. Bile acids are used therapeutically to correct deficiency states, to decrease the cholesterol saturation of bile, or to decrease the cytotoxicity of retained bile acids in cholestatic liver disease. 相似文献
395.
396.
397.
Kao WH Klag MJ Meoni LA Reich D Berthier-Schaad Y Li M Coresh J Patterson N Tandon A Powe NR Fink NE Sadler JH Weir MR Abboud HE Adler SG Divers J Iyengar SK Freedman BI Kimmel PL Knowler WC Kohn OF Kramp K Leehey DJ Nicholas SB Pahl MV Schelling JR Sedor JR Thornley-Brown D Winkler CA Smith MW Parekh RS;Family Investigation of Nephropathy Diabetes Research Group 《Nature genetics》2008,40(10):1185-1192
As end-stage renal disease (ESRD) has a four times higher incidence in African Americans compared to European Americans, we hypothesized that susceptibility alleles for ESRD have a higher frequency in the West African than the European gene pool. We carried out a genome-wide admixture scan in 1,372 ESRD cases and 806 controls and found a highly significant association between excess African ancestry and nondiabetic ESRD (lod score = 5.70) but not diabetic ESRD (lod = 0.47) on chromosome 22q12. Each copy of the European ancestral allele conferred a relative risk of 0.50 (95% CI = 0.39-0.63) compared to African ancestry. Multiple common SNPs (allele frequencies ranging from 0.2 to 0.6) in the gene encoding nonmuscle myosin heavy chain type II isoform A (MYH9) were associated with two to four times greater risk of nondiabetic ESRD and accounted for a large proportion of the excess risk of ESRD observed in African compared to European Americans. 相似文献
398.
A. F. Vanin L. M. Bevers A. Slama-Schwok E. E. van Faassen 《Cellular and molecular life sciences : CMLS》2008,65(24):4066-4069
Announcement
Announcement 相似文献399.
400.
Twigger SN Pruitt KD Fernández-Suárez XM Karolchik D Worley KC Maglott DR Brown G Weinstock G Gibbs RA Kent J Birney E Jacob HJ 《Nature genetics》2008,40(5):523-527
It has been four years since the original publication of the draft sequence of the rat genome. Five groups are now working together to assemble, annotate and release an updated version of the rat genome. As the prevailing model for physiology, complex disease and pharmacological studies, there is an acute need for the rat's genomic resources to keep pace with the rat's prominence in the laboratory. In this commentary, we describe the current status of the rat genome sequence and the plans for its impending 'upgrade'. We then cover the key online resources providing access to the rat genome, including the new SNP views at Ensembl, the RefSeq and Genes databases at the US National Center for Biotechnology Information, Genome Browser at the University of California Santa Cruz and the disease portals for cardiovascular disease and obesity at the Rat Genome Database. 相似文献