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   6774篇
  免费   560篇
  国内免费   404篇
  7738篇
  2024年   8篇
  2023年   85篇
  2022年   185篇
  2021年   323篇
  2020年   230篇
  2019年   272篇
  2018年   255篇
  2017年   198篇
  2016年   291篇
  2015年   447篇
  2014年   490篇
  2013年   530篇
  2012年   622篇
  2011年   550篇
  2010年   341篇
  2009年   303篇
  2008年   339篇
  2007年   298篇
  2006年   247篇
  2005年   204篇
  2004年   200篇
  2003年   149篇
  2002年   138篇
  2001年   125篇
  2000年   108篇
  1999年   126篇
  1998年   45篇
  1997年   55篇
  1996年   41篇
  1995年   41篇
  1994年   37篇
  1993年   37篇
  1992年   54篇
  1991年   45篇
  1990年   49篇
  1989年   40篇
  1988年   28篇
  1987年   31篇
  1986年   13篇
  1985年   18篇
  1984年   13篇
  1983年   12篇
  1982年   10篇
  1981年   10篇
  1979年   15篇
  1978年   9篇
  1974年   7篇
  1973年   11篇
  1971年   10篇
  1968年   7篇
排序方式: 共有7738条查询结果,搜索用时 15 毫秒
51.
利用甲基磺酸乙酯(EMS,ethyl methyl sulfonate)诱变剂处理野生型Yugu1(豫谷1号),在后代中发现了一个可以稳定遗传的颖花明显变窄的突变体,将其命名为sins1。与Yugu1相比,突变体sins1的株高显著降低了3.89%,穗长和穗粗分别显著降低了17.42%和21.62%,旗叶叶长和叶宽分别显著降低了15.09%和25.78%,千粒重显著降低了40.96%,谷码数显著降低了25%,均达到显著水平(P0.05)。利用突变体sins1为母本、SSR41为父本构建F_2定位群体,F_2正常颖花与窄颖花植株数目的分离比例为3∶1,表明该突变性状由隐性单基因控制。利用F_2群体隐性单株,最终将突变基因定位在3号染色体上SSR标记3-2658与CAAS3031间约7.709 Mb的距离内,为下一步精细定位提供了基础,同时也为促进禾本科作物颖花的研究提供了方向。  相似文献   
52.
Liao Yan  Chen Guizhu 《生态学报》2007,(6):2208-2214
The impact of salinity on three arboreal mangrove plants, Sonneratia apetala (Sa), S. caseolaris (Sc) and Rhizophora stylosa (Rs), was studied. The three mangrove species were treated with different salinity levels over a three-month period. The response and adaptation of these three mangrove species to salinity were shown to be different. Net photosynthesis rate, stomata conductance and transpiration rate of leaves decreased and soluble sugar content in leaves increased, with salt concentration in all three mangrove species. The malondial dehyde (MDA) content in stems and leaves of Sa and Sc somewhat decreased when the salinity was lower than 10, but rapidly increased with increasing salt concentration. The MDA content in stems and leaves of Rs increased only when salinity was greater than 40. No changes were observed in the MDA content of roots in the three mangrove species. The adaptabilities of Sa and Sc to salt tolerance were limited. The more salt tolerant the mangrove Rs, the more likely the free oxygen radicals were eliminated through the increase in activity of superoxide dismutase (SOD). Results of this experiment identified salinity levels best suited for the growth and metabolism of the species, which provides information necessary for maintaining mangrove forestation along the South China coast.  相似文献   
53.
Emodin (1,3,8-trihydroxy-6-methylanthaquinone), an active component present in the root and rhizome of Rheum palmatum L. (Polygonaceae) has anti-bacterial, anti-tumor, diuretic and vasorelaxant effects. However, its mechanism of action on the cell migration and invasion of human neuroblastoma cancer SH-SY5Y cells is not fully understood. In this study, firstly, the effects of emodin on the percentage of viable cells were examined by using MTT assay and it was found that emodin induced dose-and time-dependent inhibition in human neuroblastoma SH-SY5Y cells. Second, the effects of emodin on the migration and invasion of SH-SY5Y cells were examined by using wound assay and matrigel counting and the results showed that emodin suppressed the migration and invasion of SH-SY5Y cells. Third, we examined the effect of emodin on the levels of associated proteins by using Western blotting and the results indicated that emodin inhibited the levels of GRB2, RhoA, HIF-1α, VEGF, FAK, iNOS, COX2, p-p38, p-c-jun, MMP2, MMP9 and MMP7 but promoted the levels of PKC, PI3K, MEKK3 and NF-κB p65 that led to the inhibition of migration and invasion of SH-SY5Y cells in vitro.  相似文献   
54.
Extracellular matrix (ECM) molecules constitute a "niche" that modulates the migration, proliferation, and differentiation of neural stem/progenitor cells (NSPCs). The glycoprotein Tenascin-R (TN-R) is an ECM molecule, comprising multiple domains. Either the whole TN-R molecule or its distinct domains has been demonstrated to play a very important role in the developing central nervous system. However, little is known about the effect of the TN-R domain on NSPCs, especially NSPC migration. In the present study, we first show that both TN-R domains epidermal growth factor-like repeat (EGFL) and fibronectin type III (FN)6-8 can inhibit the NSPCs migration from neurospheres in vitro. Furthermore, both the EGFL and FN6-8 domains affect the distribution of neurons generated from neurospheres, indicating that EGFL and FN6-8 domains inhibit the motility of neurons generated from neurospheres. These results suggest that TN-R has an inhibitory effect on NSPCs migration.  相似文献   
55.
The silkworm is a lepidopteran insect that has an open circulatory system with hemolymph consisting of blood and lymph fluid. Hemolymph is not only considered as a depository of nutrients and energy, but it also plays a key role in substance transportation, immunity response, and proteolysis. In this study, we used LC‐MS/MS to analyze the hemolymph proteins of four developmental stages during metamorphosis. A total of 728 proteins were identified from the hemolymph of the second day of wandering stage, first day of pupation, ninth day of pupation, and first day as an adult moth. GO annotations and categories showed that silkworm hemolymph proteins were enriched in carbohydrate metabolism, proteolysis, protein binding, and antibacterial humoral response. The levels of nutrient, immunity‐related, and structural proteins changed significantly during development and metamorphosis. Some, such as cuticle, odorant‐binding, and chemosensory proteins, showed stage‐specific expression in the hemolymph. In addition, the expression of several antimicrobial peptides exhibited their highest level of abundance in the hemolymph of the early pupal stage. These findings provide a comprehensive proteomic insight of the silkworm hemolymph and suggest additional molecular targets for studying insect metamorphosis.  相似文献   
56.
57.
张明瑞  杨鑫  赵飞  吕莎  龚杰  周盈  李福秋 《菌物学报》2019,38(8):1235-1244
孢子丝菌复合体属于双相真菌,全球分布,可引起人类及动物的慢性深部感染。不同地域的菌株在致病力、传播途径及药物敏感性等方面均存在差异。孢子丝菌病作为一种人兽共患病,其发病率逐年上升,出现多次暴发流行。分子分型不仅是明确感染源和传播途径、预防和控制疾病流行的有力手段,同时有助于了解孢子丝菌基因型与表型的相关性,在研究其致病机制以及临床诊治过程中都具有十分重要的意义。本文对孢子丝菌的分子分型方法的研究进行综述。  相似文献   
58.
Clonal fragments of the stoloniferous herb Glechoma longituba were subjected to a complementary patchiness of light and soil nutrients including two spatially homogeneous treatments (SR–SR and IP–IP) and two spatially heterogeneous treatments (IP–SR and SR–IP). SR and IP indicate patches (shaded, rich) with low light intensity (shaded, S), high nutrient availability (rich, R) and patches (illuminated, poor) with high light intensity (illuminated, I) and low nutrient availability (poor, P), respectively. Plasticity of the species in root–shoot ratio, fitness-related traits (biomass, number of ramets and dry weight per ramet) and clonal morphological traits (length and specific length of stolon internodes, area and specific area of laminae, length and specific length of petioles) were experimentally examined. The aim is to understand adaptation of G. longituba to the environment with reciprocal patches of light and soil nutrients by plasticities both in root–shoot ratio and in (clonal) morphology. Our experiment revealed performance of the clonal fragments growing from patches with high light intensity and low soil nutrient availability into the adjacent opposite patches was increased in terms of the fitness-related characters. R/S ratio and clonal morphology were plastic. Meanwhile, the capture of light resource from the light-rich patches was enhanced while the capture of soil nutrients from either the nutrient-rich or the nutrient-poor patches was not. Analysis of cost and benefit disclosed positive effects of clonal integration on biomass production of ramets in the patches with low light intensity and high soil nutrient availability. These results suggest an existence of reciprocal translocation of assimilates and nutrients between the interconnected ramets. The reinforced performance of the clonal fragments seems to be related with specialization of clonal morphology in the species.  相似文献   
59.
杉木连栽土壤对其幼树生长的影响   总被引:6,自引:5,他引:6  
在会同林区采用3种不同连栽杉木次数的土壤,进行杉木幼树盆栽试验.结果表明,杉木连栽不利其幼树生长.连裁使幼树高生长下降37—40%,基径下降19—28%,冠幅下降21—29%,总生物量减少45—50%.杉木连栽还造成土壤养分递减,即腐殖质减少7—28%,速效养分下降23—28%,土壤微生物数量和活性也大大降低.因此,杉木纯林连栽经营方式应尽快改变.  相似文献   
60.
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