全文获取类型
收费全文 | 15570篇 |
免费 | 1534篇 |
国内免费 | 2篇 |
专业分类
17106篇 |
出版年
2024年 | 16篇 |
2023年 | 97篇 |
2022年 | 217篇 |
2021年 | 375篇 |
2020年 | 233篇 |
2019年 | 272篇 |
2018年 | 324篇 |
2017年 | 294篇 |
2016年 | 506篇 |
2015年 | 954篇 |
2014年 | 923篇 |
2013年 | 1127篇 |
2012年 | 1468篇 |
2011年 | 1403篇 |
2010年 | 894篇 |
2009年 | 767篇 |
2008年 | 995篇 |
2007年 | 993篇 |
2006年 | 946篇 |
2005年 | 903篇 |
2004年 | 859篇 |
2003年 | 737篇 |
2002年 | 679篇 |
2001年 | 112篇 |
2000年 | 69篇 |
1999年 | 113篇 |
1998年 | 135篇 |
1997年 | 76篇 |
1996年 | 71篇 |
1995年 | 53篇 |
1994年 | 54篇 |
1993年 | 52篇 |
1992年 | 36篇 |
1991年 | 45篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 31篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The Gene Ontology project (http://www.geneontology.org/) produces structured, controlled vocabularies and gene product annotations. Gene products are classified according to the cellular locations and biological process in which they act, and the molecular functions that they carry out. We annotate gene products from a broad range of model species and provide support for those groups that wish to contribute annotation of further model species. The Gene Ontology facilitates the exchange of information between groups of scientists studying similar processes in different model organisms, and so provides a broad range of opportunities for plant scientists. 相似文献
962.
We examined the effects of endogenous basic proteins rich in the amino acidL-arginine on neuronal NO synthase activity by monitoring cyclic GMP formation in intact neuron-like neuroblastoma N1E-115 cells. Histone, protamine and myelin basic protein significantly stimulated cyclic GMP formation, both in a time- and concentration-dependent manner. These effects were blocked by hemoglobin and NO synthase inhibitors. Removal of the extracellular/intracellular Ca2+ gradient by a Ca2+ chelator completely abolished the cyclic GMP responses elicited by histone and protamine, suggesting that influex of extracellular Ca2+ might be involved in their activation of NO synthase. The effects of myelin basic protein on cyclic GMP formation, however, appeared to be due to Ca2+ release from intracellular stores. In cytosolic preparations of rat cerebellum, these basic proteins inhibited the metabolism ofL-arginine intoL-citrulline by NO synthase. We conclude from our findings that endogenous basic proteins might be involved in the regulation of neuronal NO synthase activity. Their effects on the enzyme could be either stimulatory or inhibitory, depending on whether the basic proteins exert their effects extracellularly or intracellularly, respectively. 相似文献
963.
Every two months, diel depth profiles were made of dissolved oxygen, pH, temperature and conductivity at two stations in Lake Kissimmee, Florida, from July 1974 through June 1975. Results suggest that stratification does not occur in the large (137 km2), shallow (mean depth 2.5 m) lake, though steep vertical gradients in these parameters may develop. The data also suggest that when these gradients do occur, they rapidly degenerate at night or under slight wind stress. Since many Florida lakes are relatively shallow (mean depth < 5 m) and topography offers little obstruction to wind action, it is believed that the holomictic condition observed in Lake Kissimmee may be typical of the state's lakes, particularly those in the central portion of the peninsula. 相似文献
964.
965.
Environmental RNA interference 总被引:5,自引:0,他引:5
The discovery of RNA interference (RNAi), the process of sequence-specific gene silencing initiated by double-stranded RNA (dsRNA), has broadened our understanding of gene regulation and has revolutionized methods for genetic analysis. A remarkable property of RNAi in the nematode Caenorhabditis elegans and in some other multicellular organisms is its systemic nature: silencing signals can cross cellular boundaries and spread between cells and tissues. Furthermore, C. elegans and some other organisms can also perform environmental RNAi: sequence-specific gene silencing in response to environmentally encountered dsRNA. This phenomenon has facilitated significant technological advances in diverse fields including functional genomics and agricultural pest control. Here, we describe the characterization and current understanding of environmental RNAi and discuss its potential applications. 相似文献
966.
Silva C Wood JR Salvador L Zhang Z Kostetskii I Williams CJ Strauss JF 《Molecular reproduction and development》2009,76(1):11-21
Cells that morphologically and functionally resemble male germ cells can be spontaneously derived from ES cells. However, this process is inefficient and unpredictable suggesting that the expression pattern of male germ cell associated genes during spontaneous ES cell differentiation does not mimic the in vivo profiles of the genes. Thus, in the present study, the temporal profile of genes expressed at different stages of male germ cell development was examined in differentiating ES cells. The effect of all-trans retinoic acid (RA) which is a known inducer of primordial germ cell (PGC) proliferation/survival in vitro and testosterone which is required for spermatogenesis in vivo on the expression of these genes was also determined. Each of the 12 genes analyzed exhibited one of four temporal expression patterns in untreated differentiating ES cells: progressively decreased (Dppa3, Sycp3, Msy2), initially low and then increased (Stra8, Sycp1, Dazl, Act, Prm1), initially decreased and then increased (Piwil2, Tex14), or relatively unchanged (Akap3, Odf2). RA-treated cells exhibited increased expression of Stra8, Dazl, Act, and Prm1 and suppressed expression of Dppa3 compared to untreated controls. Furthermore, testosterone increased expression of Stra8 while the combination of RA and testosterone synergistically increased expression of Act. Our findings establish a comprehensive profile of male germ cell gene expression during spontaneous differentiation of murine ES cells and describe the capacity of RA and testosterone to modulate the expression of these genes. Furthermore, these data represent an important first step in designing a plausible directed differentiation protocol for male germ cells. 相似文献
967.
Paulo M. Brando Daniel C. Nepstad Jennifer K. Balch Benjamin Bolker Mary C. Christman Michael Coe Francis E. Putz 《Global Change Biology》2012,18(2):630-641
Large‐scale wildfires are expected to accelerate forest dieback in Amazônia, but the fire vulnerability of tree species remains uncertain, in part due to the lack of studies relating fire‐induced mortality to both fire behavior and plant traits. To address this gap, we established two sets of experiments in southern Amazonia. First, we tested which bark traits best predict heat transfer rates (R) through bark during experimental bole heating. Second, using data from a large‐scale fire experiment, we tested the effects of tree wood density (WD), size, and estimated R (inverse of cambium insulation) on tree mortality after one to five fires. In the first experiment, bark thickness explained 82% of the variance in R, while the presence of water in the bark reduced the difference in temperature between the heat source and the vascular cambium, perhaps because of high latent heat of vaporization. This novel finding provides an important insight for improving mechanistic models of fire‐induced cambium damage from tropical to temperate regions. In the second experiment, tree mortality increased with increasing fire intensity (i.e. as indicated by bark char height on tree boles), which was higher along the forest edge, during the 2007 drought, and when the fire return interval was 3 years instead of one. Contrary to other tropical studies, the relationship between mortality and fire intensity was strongest in the year following the fires, but continued for 3 years afterwards. Tree mortality was low (≤20%) for thick‐barked individuals (≥18 mm) subjected to medium‐intensity fires, and significantly decreased as a function of increasing tree diameter, height and wood density. Hence, fire‐induced tree mortality was influenced not only by cambium insulation but also by other traits that reduce the indirect effects of fire. These results can be used to improve assessments of fire vulnerability of tropical forests. 相似文献
968.
Huang TT Geng T Akin D Chang WJ Sturgis J Bashir R Bhunia AK Robinson JP Ladisch MR 《Biotechnology and bioengineering》2003,83(4):416-427
This work describes a simple approach to immobilize functionalized colloidal microstructures onto a C(18)-coated SiO(2) substrate via specific or non-specific bio-mediated interactions. Biotinylated bovine serum albumin pre-adsorbed onto a C(18) surface was used to mediate the surface assembly of streptavidin-coated microbeads (2.8 microm), while a bare C(18) surface was used to immobilize anti-Listeria antibody-coated microbeads (2.8 microm) through hydrophobic interactions. For a C(18) surface pre-adsorbed with bovine serum albumin, hydrophobic polystyrene microbeads (0.8 microm) and positively charged dimethylamino microbeads (0.8 microm) were allowed to self-assemble onto the surface. A monolayer with high surface coverage was observed for both polystyrene and dimethylamino microbeads. The adsorption characteristics of Escherichia coli and Listeria monocytogenes on these microbead-based surfaces were studied using fluorescence microscopy. Both streptavidin microbeads pre-adsorbed with biotinylated anti-Listeria antibody and anti-Listeria antibody-coated microbeads showed specific capture of L. monocytogenes, while polystyrene and dimethylamino microbeads captured both E. coli and L. monocytogenes non-specifically. The preparation of microbead-based surfaces for the construction of microfluidic devices for separation, detection, or analysis of specific biological species is discussed. 相似文献
969.
Fungal genomics revealed a large potential of yet-unexplored secondary metabolites, which are not produced during vegetative growth. The discovery of novel bioactive compounds is increasingly gaining importance. The high number of resistances against established antibiotics requires novel drugs to counteract increasing human and animal mortality rates. In addition, growth of plant pathogens has to be controlled to minimize harvest losses. An additional critical issue is the post-harvest production of deleterious mycotoxins. Fungal development and secondary metabolite production are linked processes. Therefore, molecular regulators of development might be suitable to discover new bioactive fungal molecules or to serve as targets to control fungal growth, development, or secondary metabolite production. The fungal impact is relevant as well for our healthcare systems as for agriculture. We propose here to use the knowledge about mutant strains discovered in fungal model systems for a broader application to detect and explore new fungal drugs or toxins. As examples, mutant strains impaired in two conserved eukaryotic regulatory complexes are discussed. The COP9 signalosome (CSN) and the velvet complex act at the interface between development and secondary metabolism. The CSN is a multi-protein complex of up to eight subunits and controls the activation of CULLIN-RING E3 ubiquitin ligases, which mark substrates with ubiquitin chains for protein degradation by the proteasome. The nuclear velvet complex consists of the velvet-domain proteins VeA and VelB and the putative methyltransferase LaeA acting as a global regulator for secondary metabolism. Defects in both complexes disturb fungal development, light perception, and the control of secondary metabolism. The potential biotechnological relevance of these developmental fungal mutant strains for drug discovery, agriculture, food safety, and human healthcare is discussed. 相似文献
970.
Teitz T Stanke JJ Federico S Bradley CL Brennan R Zhang J Johnson MD Sedlacik J Inoue M Zhang ZM Frase S Rehg JE Hillenbrand CM Finkelstein D Calabrese C Dyer MA Lahti JM 《PloS one》2011,6(4):e19133