全文获取类型
收费全文 | 768篇 |
免费 | 56篇 |
专业分类
824篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 26篇 |
2015年 | 36篇 |
2014年 | 37篇 |
2013年 | 33篇 |
2012年 | 50篇 |
2011年 | 63篇 |
2010年 | 49篇 |
2009年 | 26篇 |
2008年 | 43篇 |
2007年 | 47篇 |
2006年 | 47篇 |
2005年 | 36篇 |
2004年 | 42篇 |
2003年 | 28篇 |
2002年 | 44篇 |
2001年 | 15篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 6篇 |
1993年 | 13篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有824条查询结果,搜索用时 15 毫秒
1.
Interannual variability of phytoplankton productivity and related parameters in Lake Constance: no response to decreased phosphorus loading? 总被引:2,自引:0,他引:2
Tilzer Max M.; Gaedke Ursula; Schweizer Anette; Beese B?rbel; Wieser Thomas 《Journal of plankton research》1991,13(4):755-777
In meso-eutrophic Lake Constance (Germany-Austria-Switzerland),phytoplankton bioraass, pigments and water transparency, aswell as primary productivity, have been followed between 1980and 1989. During this period, municipal phosphorus loading declinedsignificantly. Since 1981, soluble reactive phosphorus (SRP)concentrations during deep lake mixing have decreased from 3.0to currently 1 6 mmol m3 at a rate of 7% year1.Nitrate concentrations, by contrast, continued to rise. Duringthe period of maximum phosphorus loading, flushing through theoutlet and sedimentation were about equally important sinksof phosphorus from the euphotic zone. Recently, however, sedimentationand subsequent burial of P in the bottom deposits contributedabout three-quarters to the overall P-losses from the systemMain reasons for this shift are unchanged settling fluxes ofphosphorus out of the euphotic zone and decreasing concentrationsof total phosphorus in the water. Only during spring, do concentrations of soluble reactive phosphoruswithin the euphotic zone decrease in proportion to the formationof particulate organic matter. Later during the season, euphoticSRP concentrations continue to be low but are no longer matchedby high plankton biomass because phosphorus is efficiently removedby settling of particles In spite of the observed dramatic decreasein phosphorus loading since 1980, chlorophyll concentrationsand water transparency, as well as annual phytoplankton productivity(300 g C m2), have not shown a consistent downward trend.However, the intensity of phosphorus regeneration within theeuphoric zone, which can be used as a measure of the degreeof nutrient limitation, is likely to have increased significantlyThe most probable explanation for the insensitivity of importanttrophic state indicators to reduced nutrient loading is that,in Lake Constance, biomass accumulation to a greater extentis controlled by losses, mainly grazing by zooplankton and sedimentation,than by primary resources. This is concluded from the observationthat phytoplankton biomass always falls far short of the nutrient-dependentcarrying capacity of the system. 相似文献
2.
3.
4.
Staphylococcal infections that result from an alteration in a patient's immune response at the surgical site are a major
problem in procedures that incorporate biomaterials in trauma surgery and joint replacement. Diagnosis of infection based
on pathogen detection is difficult and exacerbated by increasing numbers of partially or totally resistant strains of nosocomial
pathogens, particularly Staphylococcus aureus. Expression profiling of a host's cellular immune response could facilitate the identification of the pathways involved in
pathogen recognition and eradication and could lead to more rational design of drugs and therapies. To this end, we constructed
and characterized ten individually tagged and directionally cloned cDNA libraries from peripheral blood cells (PBC), spleen
(Sp), thymus (Th), lymph node (LN), and bone marrow (BM) from immunologically naive and challenged pigs as part of an implant-associated
orthopedic model of deep infection. Three of these libraries were normalized at C
0
t
values 5, 10, 20, and 30. The libraries comprise more than 20 million primary transformants with an average insert length
>1.4 kb. Cluster analysis of 7620 ESTs revealed 1029 clusters containing an average of 3.6 sequences and 3846 singletons.
Gene discovery is estimated to be ∼64%. Searches of public databases resulted in 49.3% annotated porcine sequences, of which
22.2% had significant homologies to ESTs from a variety of species, and 28.5% were without a significant match in any public
database. We also identified 9.1% ESTs as involved in host cell and organism defense and 11.5% related to cell signaling and
communication. These sequences, together with the 28.5% appearing as novel, are of specific interest to the infectious disease
process. 相似文献
5.
6.
7.
8.
Grundström S Cederbom L Sundstedt A Scheipers P Ivars F 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(10):5008-5017
Repeated exposures to both microbial and innocuous Ags in vivo have been reported to both eliminate and tolerize T cells after their initial activation and expansion. The remaining tolerant T cells have been shown to suppress the response of naive T cells in vitro. This feature is reminiscent of natural CD4(+)CD25(+) regulatory T cells. However, it is not known whether the regulatory function of in vivo-tolerized T cells is similar to the function of natural CD4(+)CD25(+) regulatory T cells. In this study, we demonstrate that CD4(+)CD25(+) as well as CD4(+)CD25(-) T cells isolated from mice treated with superantigen three consecutive times to induce tolerance were functionally comparable to natural CD4(+)CD25(+) regulatory T cells, albeit more potent. The different subpopulations of in vivo-tolerized CD4(+) T cells efficiently down-modulated costimulatory molecules on dendritic cells, and their suppressive functions were strictly cell contact dependent. Importantly, we demonstrate that conventional CD4(+)CD25(-) T cells could also be induced to acquire regulatory functions by the same regimen in the absence of natural regulatory T cells in vivo, but that such regulatory cells were functionally different. 相似文献
9.
Sørensen GL Hjelmborg Jv Kyvik KO Fenger M Høj A Bendixen C Sørensen TI Holmskov U 《American journal of physiology. Lung cellular and molecular physiology》2006,290(5):L1010-L1017
The collectin surfactant protein D (SP-D) is an important component of the pulmonary innate immune system, but SP-D is also present on extrapulmonary epithelial surfaces and in serum, where it has been used as a biomarker for pulmonary disease states. In this study, we investigate the mechanisms defining the constitutional serum level of SP-D and determine the magnitude of the genetic contribution to serum SP-D in the adult population. Recent studies have demonstrated that serum SP-D concentrations in children are genetically determined and that a single nucleotide polymorphism (SNP) located in the NH(2)-terminal region (Met11Thr) of the mature protein is significantly associated with the serum SP-D levels. A classic twin study was performed on a twin population including 1,476 self-reported healthy adults. The serum SP-D levels increased with male sex, age, and smoking status. The intraclass correlation was significantly higher for monozygotic (MZ) twin pairs than for dizygotic (DZ) twin pairs. Serum SP-D variance was influenced by nonshared environmental effects and additive genetic effects. Multivariate analysis of MZ and DZ covariance matrixes showed significant genetic correlation among serum SP-D and metabolic variables. The Met11Thr variant explained a significant part of the heritability indicating that serum SP-D variance could be decomposed into non-shared environmental effects (e(2) = 0.19), additive genetic effects (h(2) = 0.42), and the effect of the Met11Thr variations (q(2) = 0.39). 相似文献
10.
Vegard?Bruun?WyllerEmail author Even?Fagermoen Dag?Sulheim Anette?Winger Eva?Skovlund Jerome?Philip?Saul 《BioPsychoSocial medicine》2014,8(1):22