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881.
Biodiversity as a barrier to ecological invasion 总被引:69,自引:0,他引:69
Biological invasions are a pervasive and costly environmental problem that has been the focus of intense management and research activities over the past half century. Yet accurate predictions of community susceptibility to invasion remain elusive. The diversity resistance hypothesis, which argues that diverse communities are highly competitive and readily resist invasion, is supported by both theory and experimental studies conducted at small spatial scales. However, there is also convincing evidence that the relationship between the diversity of native and invading species is positive when measured at regional scales. Although this latter relationship may arise from extrinsic factors, such as resource heterogeneity, that covary with diversity of native and invading species at large scales, the mechanisms conferring greater invasion resistance to diverse communities at local scales remain unknown. Using neighbourhood analyses, a technique from plant competition studies, we show here that species diversity in small experimental grassland plots enhances invasion resistance by increasing crowding and species richness in localized plant neighbourhoods. Both the establishment (number of invaders) and success (proportion of invaders that are large) of invading plants are reduced. These results suggest that local biodiversity represents an important line of defence against the spread of invaders. 相似文献
882.
883.
Nonlinear grassland responses to past and future atmospheric CO(2) 总被引:17,自引:0,他引:17
Carbon sequestration in soil organic matter may moderate increases in atmospheric CO(2) concentrations (C(a)) as C(a) increases to more than 500 micromol mol(-1) this century from interglacial levels of less than 200 micromol mol(-1) (refs 1 6). However, such carbon storage depends on feedbacks between plant responses to C(a) and nutrient availability. Here we present evidence that soil carbon storage and nitrogen cycling in a grassland ecosystem are much more responsive to increases in past C(a) than to those forecast for the coming century. Along a continuous gradient of 200 to 550 micromol mol(-1) (refs 9, 10), increased C(a) promoted higher photosynthetic rates and altered plant tissue chemistry. Soil carbon was lost at subambient C(a), but was unchanged at elevated C(a) where losses of old soil carbon offset increases in new carbon. Along the experimental gradient in C(a) there was a nonlinear, threefold decrease in nitrogen availability. The differences in sensitivity of carbon storage to historical and future C(a) and increased nutrient limitation suggest that the passive sequestration of carbon in soils may have been important historically, but the ability of soils to continue as sinks is limited. 相似文献
884.
Neutrophil elastase targets virulence factors of enterobacteria 总被引:14,自引:0,他引:14
Shigellae cause bacillary dysentery, a bloody form of diarrhoea that affects almost 200 million people and causes nearly 2 million deaths per year. Shigella invades the colonic mucosa, where it initiates an acute inflammation, rich in neutrophils, that initially contributes to tissue damage and eventually resolves the infection. Neutrophils are phagocytic cells that kill microorganisms but it is unclear how neutrophils control pathogenic bacteria expressing virulence factors that manipulate host cells. In contrast to other cells, neutrophils prevent the escape of Shigella from phagocytic vacuoles in which the bacteria are killed. Here we identify human neutrophil elastase (NE) as a key host defence protein: NE degrades Shigella virulence factors at a 1,000-fold lower concentration than that needed to degrade other bacterial proteins. In neutrophils in which NE is inactivated pharmacologically or genetically, Shigella escapes from phagosomes, increasing bacterial survival. NE also preferentially cleaves virulence factors of Salmonella and Yersinia. These findings establish NE as the first neutrophil factor that targets bacterial virulence proteins. 相似文献
885.
886.
887.
Bejaoui K Wu C Scheffler MD Haan G Ashby P Wu L de Jong P Brown RH 《Nature genetics》2001,27(3):261-262
Hereditary sensory neuropathy type 1 (HSN1, MIM 162400; ref. 1) genetically maps to human chromosome 9q22 (refs. 2-4). We report here that the gene encoding a subunit of serine palmitoyltransferase is located within the HSN1 locus, expressed in dorsal root ganglia (DRG) and mutated in HSN1. 相似文献
888.
889.
Arginase expression in peritoneal macrophages and increase in circulating polyamine levels in mice infected with Schistosoma mansoni 总被引:5,自引:0,他引:5
Abdallahi OM Bensalem H Augier R Diagana M De Reggi M Gharib B 《Cellular and molecular life sciences : CMLS》2001,58(9):1350-1357
We investigated the nitric oxide (NO) synthase and arginase pathways in resident peritoneal macrophages of mice infected
with the tropical parasite Schistosoma mansoni. The two enzymes may have opposite effects, insofar as NO may be involved in the killing of the parasite whereas arginase
may stimulate parasite growth via polyamine synthesis. We determined the effects of the infection on the expression and activity
of the two enzymes in macrophages, before and after cytokine activation. Cells from infected mice expressed the hepatic type
I arginase, whereas in control cells, the enzyme was expressed only after cytokine activation, as were NO synthase II and
type II arginase in both groups of cells. Moreover, we found that in infected mice, arginase expression in macrophages was
associated with a ten fold increase in the concentration of circulating ornithine-derived polyamines. This may be of pathological
importance, since parasitic helminths are though to be dependent on their hosts for the uptake and interconversion of polyamines.
Received 13 March 2001; received after revision 4 May 2001; accepted 7 June 2001 相似文献
890.
Recombinant expression of perchloric acid-soluble protein reduces cell proliferation 总被引:3,自引:0,他引:3
Kanouchi H Tachibana H Oka T Yamada K 《Cellular and molecular life sciences : CMLS》2001,58(9):1340-1343
Perchloric acid-soluble protein (PSP) may play an important role in the regulation of cellular physiological functions because
it has been highly conserved throughout evolution; however, this role has not been well elucidated. In previous reports, we
suggested that PSP regulates cell proliferation. In this study, we examined the effect of PSP expression on proliferation
of the normal rat kidney cell line NRK-52E, the rat hepatocyte cell line RLN-10, and the rat hepatoma cell line dRLh-84. Cells
transfected with pcDNA-sense-PSP (pcDNA-S-PSP) over-expressed PSP mRNA and protein, and cell proliferation of the transfected
cells was suppressed compared with that of cells transfected with pcDNA-empty (pcDNA-E). Cell viability of pcDNA-S-PSP-transfected
cells was similar to that of pcDNA-E-transfected cells. Thus, over-expression of PSP suppresses cell proliferation without
any influence on cell viability. These findings are the first to report an inhibitory activity of PSP on cell proliferation.
Received 27 April 2001; received after revision 8 June 2001; accepted 8 June 2001 相似文献