全文获取类型
收费全文 | 4509篇 |
免费 | 519篇 |
国内免费 | 2篇 |
专业分类
5030篇 |
出版年
2023年 | 35篇 |
2022年 | 52篇 |
2021年 | 107篇 |
2020年 | 70篇 |
2019年 | 52篇 |
2018年 | 61篇 |
2017年 | 79篇 |
2016年 | 137篇 |
2015年 | 247篇 |
2014年 | 254篇 |
2013年 | 255篇 |
2012年 | 348篇 |
2011年 | 316篇 |
2010年 | 205篇 |
2009年 | 196篇 |
2008年 | 277篇 |
2007年 | 233篇 |
2006年 | 226篇 |
2005年 | 241篇 |
2004年 | 218篇 |
2003年 | 207篇 |
2002年 | 195篇 |
2001年 | 60篇 |
2000年 | 59篇 |
1999年 | 53篇 |
1998年 | 65篇 |
1997年 | 47篇 |
1996年 | 38篇 |
1995年 | 30篇 |
1994年 | 35篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 32篇 |
1990年 | 34篇 |
1989年 | 31篇 |
1988年 | 32篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 31篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 18篇 |
1977年 | 25篇 |
1976年 | 17篇 |
1974年 | 14篇 |
1973年 | 17篇 |
排序方式: 共有5030条查询结果,搜索用时 0 毫秒
961.
Lars Kristian Munck Marie Louise Grndahl Jens Erik Thorbll Erik Skadhauge Bjarne Gyldenlve Munck 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2000,126(4)
Amino acid influx across the brush border membrane of the intact pig ileal epithelium was studied. It was examine whether in addition to system B, systems ASC and bo,+ were involved in transport of bipolar amino acids. The kinetics of interactions between lysine and leucine demonstrates that system bo,+ is present and accessible also to
-glutamine.
-aspartate (K1/2 0.3 mM) and
-glutamate (Ki 0.5 mM) share a high affinity transporter with a maximum rate of 1.3 μmol cm−2 h−1, while only
-glutamate with a K1/2 of 14.4 mM uses a low affinity transporter with a maximum rate of 2.7 μmol cm−2 h−1, system ASC, against which serine has a Ki of 1.6 mM. In the presence of 100 mM lysine,
-glutamine (A), leucine (B), and methionine (C) fulfilled the criteria of the ABC test for transport by one and the same transporter. However, serine inhibits not only transport of
-glutamate but also of glutamine (Ki 0.5 mM), and
-glutamate inhibits part of the transport of glutamine. The test does, therefore, only indicate that the three bipolar amino acids have similar affinities for transport by systems B and ASC. Further study of the function of system B must be carried out under full inhibition by lysine and glutamate. 相似文献
962.
Louise Cramer 《Genome biology》2000,1(1):reports404.1-1
A report on work presented at the 39th Annual Meeting of the American Society for Cell Bilogy, Washington DC, December 11-15, 1999 相似文献
963.
Hypoxia acts as an important regulator of physiological and pathological processes. Hypoxia inducible factors (HIFs) are the central players involved in the cellular adaptation to hypoxia and are regulated by oxygen sensing EGLN prolyl hydroxylases. Hypoxia affects many aspects of cellular growth through both redox effects and through the stabilization of HIFs. The HIF isoforms likely have differential effects on tumor growth via alteration of metabolism, growth, and self-renewal and are likely highly context-dependent. In some tumors such as renal cell carcinoma, the EGLN/HIF axis appears to drive tumorigenesis, while in many others HIF1 and HIF2 may actually have a tumor suppressive role. An emerging role of HIF biology is its effects on the tumor microenvironment. The EGLN/HIF axis plays a key role in regulating the function of the various components of the tumor microenvironment, which include cancer-associated fibroblasts, endothelial cells, immune cells, and the extracellular matrix (ECM). Here, we discuss hypoxia and the diverse roles of HIFs in the setting of tumorigenesis and the maintenance of the tumor microenvironment as well as possible future directions of the field. 相似文献
964.
Xin Gao Yurong R. Cao Nicholas Ogden Louise Aubin Huaiping P. Zhu 《Biometrical journal. Biometrische Zeitschrift》2017,59(3):462-477
A mixture Markov regression model is proposed to analyze heterogeneous time series data. Mixture quasi‐likelihood is formulated to model time series with mixture components and exogenous variables. The parameters are estimated by quasi‐likelihood estimating equations. A modified EM algorithm is developed for the mixture time series model. The model and proposed algorithm are tested on simulated data and applied to mosquito surveillance data in Peel Region, Canada. 相似文献
965.
Mechanistic insight into nuclear receptor‐mediated regulation of bile acid metabolism and lipid homeostasis by grape seed procyanidin extract (GSPE) 下载免费PDF全文
Laura E. Downing Daniel Edgar Patricia A. Ellison Marie‐Louise Ricketts 《Cell biochemistry and function》2017,35(1):12-32
Dietary procyanidins have emerged as important bioactive components that regulate various metabolic pathways to maintain homeostasis. Grape seed procyanidin extract (GSPE), in particular, has demonstrated regulatory effects on bile acid and lipid metabolism in vivo. While numerous studies in rodent models have shown the potent hypolipidemic action of grape seed extracts, human studies have shown inconsistent results. This review will focus on the molecular mechanisms underlying the hypolipidemic actions of GSPE identified to date, specifically highlighting the effects exerted via nuclear receptors. Such evidence may provide avenues for future research in human subjects with GSPE as a therapeutic treatment for the prevention and amelioration of the metabolic syndrome and cardiovascular disease. 相似文献
966.
967.
Vlado Buljan Karen M Cullen 《Biochemical and biophysical research communications》2009,381(2):224-228
Here we show a new effect of Ca2+ on microtubule morphology: Ca2+ can cause smooth curving of microtubules in the presence of microtubule-associated proteins (MAPs). In vitro, microtubules self-organize, forming complex dissipative structures. Such structures may be strongly affected by relatively weak external factors. A factor such as Ca2+ potentially influences spatiotemporal patterns of microtubule assembly, but the dynamics are unclear. We tested Ca2+ effects on microtuble formation. Using EM, microtubule length, curvature, and alignment and were measured in two systems: 2 mg/ml microtubule protein containing MAPs and 1 mM EGTA with and without 1 mM Ca2+. The two systems were then tested using light scattering. In low Ca2+, a birefringent microtubular pattern is seen, increasing with polymerization. When 1 mM Ca2+ is added to the solution. anisotropic phase is prevented without microtubule disruption. This demonstrates an additional mechanism by which Ca2+ can alter the dynamics and morphology of microtules. 相似文献
968.
Louise Kasprowicz Gaynor Malloch Jon Pickup Brian Fenton 《Agricultural and Forest Entomology》2008,10(2):91-100
1 The population of peach‐potato aphid Myzus persicae in Scotland is comprised almost entirely of long‐term asexual clones. 2 Over a ten year period, M. persicae from Scottish fields and suction traps were analysed with six microsatellite markers. 3 Out of 1497 individuals analysed, 14 clones (denoted A–N) comprised over 98% of the collection. 4 Some clones were particularly abundant but most clones had a widespread distribution on all available plants. 5 Clones E and L had distinct features in their distributions as clone L was geographically totally restricted to the north east of Scotland and clone E showed a marked preference for brassica crops. 6 Clones E and L provide direct evidence of a role for local adaptations in the distribution of M. persicae clones. 相似文献
969.
Detrimental interactions between marine mammals and fisheries are increasing worldwide. The ability to manage these interactions
requires the knowledge of where and how interactions occur and the effects they have on species. Many pinnipeds are central
place foraging colonial breeders who are restricted in foraging range during breeding. Here, we use a utilization distribution
approach to examine the foraging habitats of lactating New Zealand (NZ) sea lions (Phocarctos hookeri) from Dundas and Enderby Islands, Auckland Islands. Annually, the NZ sea lions which breed on these two islands produce 83%
of this Nationally Critical species’ pups. Satellite transmitters were attached to 55 females during 2001–2007. Data showed
that NZ sea lions utilize the entire Auckland Island shelf with partial habitat partitioning between females from the two
breeding islands. This habitat partitioning results in differing degrees of overlap with fisheries and therefore possible
differing fishery-related impacts on breeding areas. 相似文献
970.
Louise A Jopling Ian Sabroe David P Andrew Tracey J Mitchell You Li Martin R Hodge Timothy J Williams James E Pease 《The Journal of biological chemistry》2002,277(9):6864-6873
Th2 lymphocytes play a central role in the control and maintenance of allergic inflammation. The chemokine receptor CCR4 is preferentially expressed on the surface of Th2 lymphocytes polarised in vitro. However, CCR4 is found on the surface of a significant proportion of circulating memory T lymphocytes, some of which are capable of producing the Th1-associated cytokine interferon gamma. To investigate the function of CCR4 on guinea pig (gp) T lymphocytes, we identified the open-reading frame of gpCCR4, which encodes a 361-amino acid protein with 88 and 81% amino acid identity to human and murine CCR4 sequences, respectively. Cells transfected with gpCCR4 migrated toward the human and murine orthologues of the CCR4 ligands, macrophage-derived chemokine and thymus and activation-regulated chemokine. Surface expression of CCR4, using an anti-human CCR4 monoclonal antibody, 10E4, was detected on approximately 12% of guinea pig peripheral blood T helper cells, and CCR4(+) guinea pig thymocytes were detected in low numbers. However, CCR4(+) T helper cells constituted approximately 9% of the T lymphocyte population within the normal guinea pig lung and 52% of the guinea pig bronchoalveolar lavage fluid, which is consistent with a role for CCR4 in T lymphocyte development and trafficking through normal tissues. Subsequent analysis of chimeric chemokine receptors indicated that 10E4, a functional inhibitor of gpCCR4 responses, recognized the amino terminus of CCR4. 相似文献