首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2410篇
  免费   109篇
  国内免费   3篇
  2022年   7篇
  2021年   12篇
  2020年   6篇
  2019年   9篇
  2018年   12篇
  2017年   18篇
  2016年   26篇
  2015年   39篇
  2014年   74篇
  2013年   391篇
  2012年   97篇
  2011年   122篇
  2010年   91篇
  2009年   63篇
  2008年   137篇
  2007年   138篇
  2006年   126篇
  2005年   154篇
  2004年   159篇
  2003年   142篇
  2002年   149篇
  2001年   23篇
  2000年   11篇
  1999年   27篇
  1998年   29篇
  1997年   25篇
  1996年   32篇
  1995年   24篇
  1994年   13篇
  1993年   22篇
  1992年   21篇
  1991年   24篇
  1990年   16篇
  1989年   11篇
  1988年   17篇
  1987年   9篇
  1986年   10篇
  1985年   14篇
  1984年   19篇
  1983年   12篇
  1982年   24篇
  1981年   30篇
  1980年   22篇
  1979年   10篇
  1978年   15篇
  1977年   15篇
  1976年   14篇
  1975年   11篇
  1974年   13篇
  1973年   6篇
排序方式: 共有2522条查询结果,搜索用时 31 毫秒
961.
We examined the effect of the inflammatory mediator interleukin-1alpha (IL-1alpha) on cell proliferation, alkaline phosphatase (ALPase) activity, and the expressions of cartilage matrix proteins, bone morphogenetic protein-2 (BMP-2), and BMP-2 receptors in human chondrosarcoma cell line OUMS-27 (chondrocytes). The cells were cultured with Dulbecco's modified Eagle's medium containing 15% fetal bovine serum with 0, 1, 10, or 100 units/ml of IL-1alpha for up to 14 days. The expressions of cartilage matrix proteins, BMP-2, and BMP-2 receptors were estimated by determining mRNA levels using semiquantitative or real-time PCR and/or by determining protein levels using Enzyme-linked immunosorbent assay. Cell proliferation was decreased after 5 days in culture with IL-1alpha. The ALPase activity was decreased significantly in the presence of IL-1alpha until day 10 of culture. The expression of type II collagen was significantly decreased after 7 days in culture with IL-1alpha. The expressions of aggrecan and link protein were significantly decreased through day 14 of culture with IL-1alpha. The expression of BMP-2 was increased at days 3, 7, and 14 of culture with IL-1alpha, while the expression of type II receptor for BMP-2 was significantly decreased in the samples. These results suggest that IL-1alpha suppresses the expression of cartilage matrix proteins through a suppression of the autocrine action of BMP-2, brought about by the decrease in BMP-2 receptor expression in chondrocytes.  相似文献   
962.
963.
Bluegill (Lepomis macrochirus) in Lake Biwa, Japan, feed on benthic invertebrates (benthivorous type), aquatic plants (herbivorous type), and zooplankton (planktivorous type). To evaluate the effect of food on intestinal bacterial microbiota, we characterized and compared the intestinal microbiota of these three types of bluegill in terms of community-level physiological profile (CLPP) and genetic structure. The CLPP was analyzed using Biolog MicroPlates (Biolog, Inc., Hayward, CA, USA), and multivariate analysis of variance revealed that the CLPP of intestinal microbiota differed significantly between any pairs of the three types of bluegill. The genetic profiles were analyzed by temperature gradient gel electrophoresis of polymerase chain reaction (PCR)-amplified 16S rDNA fragments, and multidimensional scaling indicated the existence of specific intestinal bacterial structures for both the benthivorous and the planktivorous types. These results suggest that the host's feeding habit can be one factor controlling the intestinal microbiota of fish in the natural environment.  相似文献   
964.
965.
The effect of cAMP on prostaglandin production may depend on cell types. To clarify the relationship between PG and cAMP, we examined arachidonate's effects on PG synthesis and intracellular cAMP accumulation in monolayers of rat gastric mucosal cells. These cells produced PGE2, PGI2 and thromboxaneA2 (TXA2) in amounts of 316±18, 100±7 and 30±5 pg per 105 cells in 10 min, respectively, in response to 10μM arachidonic acid (AA). The production of these PG, however, leveled off subsequently. Cells initially exposed to AA responded poorly to a subsequent stimulation by AA. AA simultaneously stimulated intracellular cAMP accumulation; this stimulatory effect on cAMP production was abolished by the pretreatment with indomethacin. Nevertheless, the pretreatments with dibutyryl cAMP (0.1–5mM) did not alter the amount of subsequent AA-induced PGE2 production. Furthermore, the preincubation with 1mM isobutyl methyl xanthine also failed to affect PGE2 synthesis, while it increased intracellular cAMP accumulation. Our studies suggest (1) AA stimulates intracellular cAMP formation in cultured gastric mucosal cells, linked with conversion of AA to cyclooxygenase metabolites, (2) AA-induced PG production is limited in these cells, and (3) it seems, however, unlikely that intracellular cAMP modulates AA metabolism to PG.  相似文献   
966.
Feline immunodeficiency virus (FIV) was isolated from a wild-caught Tsushima cat (Felis bengalensis euptilura), an endangered Japanese nondomestic subspecies of leopard cat (F. bengalensis). Phylogenetic analysis of the env gene sequences indicated that the FIV from the Tsushima cat belonged to a cluster of subtype D FIVs from domestic cats. FIVs from both the Tsushima cat and the domestic cat showed similar levels of replication and cytopathicity in lymphoid cell lines derived from these two species. The results indicated the occurrence of interspecies transmission of FIV from the domestic cat to the Tsushima cat in the wild.  相似文献   
967.
To predict outbreaks of infectious disease and to prevent epidemics, it is essential not only to conduct pathological studies but also to understand the interactions between the environment, pathogen, host and humans that cause and spread infectious diseases. Outbreaks of mass mortality in carp caused by Cyprinid herpesvirus 3 (CyHV-3), formerly known as koi herpesvirus (KHV), disease have occurred worldwide since the late 1990s. We proposed an environment?CKHV?Ccarp?Chuman linkage as a conceptual model for ??environmental diseases?? and specify research subjects that might be necessary to construct and shape this linkage.  相似文献   
968.
Floral scent chemistry of mangrove plants   总被引:2,自引:0,他引:2  
The flowers of mangrove plants are pollinated by a variety of pollinators including birds, bats, and insects. This study analyzed the floral scent chemistry of mangroves on Iriomote Island (located near Taiwan) including Bruguiera gymnorrhiza (L.) Lamk. (Rhizophoraceae), Kandelia candel (L.) Druce (Rhizophoraceae), Rhizophora stylosa Griff. (Rhizophoraceae), Sonneratia alba J. Smith (Sonneratiaceae), Nypa fruticans (Thunb.) Wurmb. (Palmae), Lumnitzera racemosa Willd. (Combretaceae), Avicennia marina (Forsk.) Vierh. (Avicenniaceae or Verbenaceae), and Pemphis acidula Forst. (Lythraceae). A total of 61 chemicals (fatty acid derivatives, terpenoids, carotenoid derivatives, benzenoids, nitrogen-containing compounds, 13 unknown chemicals) were detected in the floral scents of the various species. The species displayed a distinct chemical profile ranging from only two chemicals in the floral scent of Kandelia candel to more than 25 chemicals in the floral scent of Nypa fruticans. All of the identified chemicals have been found in the floral scents of other angiosperms. The chemical profile of some species can be correlated with their floral morphology and pollinators.  相似文献   
969.
Simultaneous monitoring of amperometric currents at a glass capillary sensor based on recombinant GluOx and field excitatory postsynaptic potentials (fEPSPs) were performed in region CA1 of mouse hippocampal slices. A transient increase in the glutamate current relative to the basal one at control stimulation (0.052Hz) was evoked by stimulation at 2 Hz for 2 min. The magnitude of the glutamate current was dependent on the intensity (current) of a 2 Hz stimulus and reflected the slope of the fEPSP. The in situ calibration of the L-glutamate sensor revealed that the extracellular concentration of L-glutamate released by 2 Hz stimulation before tetanus is in the range from 0.8 to 2.2 μM and it is enhanced after tetanic stimulation. The L-glutamate level at a test stimulus (0.052 Hz) was estimated to be 32 nM. The recombinant GluOx-based sensor exhibited weak responses to glutamine above 300 μM and L-aspartic acid above 200 μM. The potential use of a glass capillary sensor in combination with fEPSP measurements for electrophysiological study is discussed.  相似文献   
970.
The rice (Oryza sativa L.) catalase (EC 1.11.1.6) gene CatB is expressed in roots and cultured cells. We examined the promoter activity of its 5'-flanking region in a monocot and in two dicots. Transient expression assays in rice Oc and tobacco BY-2 suspension cell protoplasts showed that CatB's 5'-flanking DNA fragments (nucleotides -1066 to +298) had about 20 and 3-4 times as much promoter activity, respectively, as the CaMV 35S promoter. Serial deletion analyses of the CatB promoter region revealed that the shortest fragment (-56 to +298) still had about 10 times as much promoter activity as the CaMV 35S promoter in rice protoplasts. In tobacco protoplasts, the activity of the fragment (-56 to +298) was about half of the CaMV 35S promoter. Transgenic rice and Arabidopsis plants carrying GUS genes driven by the 5'-truncated CatB promoters were generated and their GUS activity was examined. The region ranging from -329 to +298 showed preferential expression in the roots of rice and Arabidopsis, and in the shoot apical meristems of Arabidopsis. In situ hybridization revealed that CatB was highly expressed in branch root primordia and root apices of rice. Fusion of the GUS gene to the region (-329 to +298) conferred strong expression in these same areas, indicating that the presence of this region was sufficient to express CatB specifically in the roots. There may be new regulatory element(s) in this region, because it contained no previously known cis-regulatory elements specific for gene expression in roots.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号