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   19602篇
  免费   1543篇
  国内免费   1072篇
  2024年   43篇
  2023年   240篇
  2022年   383篇
  2021年   439篇
  2020年   652篇
  2019年   795篇
  2018年   873篇
  2017年   643篇
  2016年   688篇
  2015年   616篇
  2014年   1044篇
  2013年   1556篇
  2012年   589篇
  2011年   971篇
  2010年   717篇
  2009年   940篇
  2008年   952篇
  2007年   998篇
  2006年   932篇
  2005年   867篇
  2004年   749篇
  2003年   662篇
  2002年   632篇
  2001年   432篇
  2000年   321篇
  1999年   351篇
  1998年   376篇
  1997年   334篇
  1996年   349篇
  1995年   318篇
  1994年   305篇
  1993年   220篇
  1992年   235篇
  1991年   209篇
  1990年   151篇
  1989年   175篇
  1988年   129篇
  1987年   132篇
  1986年   124篇
  1985年   138篇
  1984年   195篇
  1983年   129篇
  1982年   148篇
  1981年   102篇
  1980年   115篇
  1979年   82篇
  1978年   29篇
  1977年   40篇
  1976年   36篇
  1974年   24篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Conjugational transfer of pLS20 in Bacillus subtilis Marburg 168 is restricted by the BsuM restriction-modification system. Restriction efficiency was measured using pLS20 derivatives possessing various numbers of XhoI sites, which are known to be recognized by BsuM. An increase in XhoI sites clearly reduced the conjugational efficiency of pLS20 as compared with that of pUB110 plasmid lacking XhoI.  相似文献   
2.
Energy storage in arthropods has important implications for survival and reproduction. The lipid content of 276 species of adult arthropods with wet mass in the range 0.2–6.13 g is determined to assess how lipid mass scales with body mass. The relative contribution of lipids to total body mass is investigated with respect to phylogeny, ontogeny and sex. The lipid content of adult insects, arachnids, and arthropods in general shows an isometric scaling relationship with respect to body mass (M) (Marthropod lipid = ?1.09 ×Mdry1.01 and Marthropod lipid = ?1.00 ×Mlean0.98). However, lipid allocation varies between arthropod taxa, as well as with sex and developmental stage within arthropod taxa. Female insects and arachnids generally have higher lipid contents than males, and larval holometabolous insects and juvenile arachnids have higher lipid contents than adults.  相似文献   
3.
The allelopathic potential of the dry fruits of Washingtonia filifera (L. Linden) H. Wendl. was investigated. Leachates from fruits inhibited the germination of lettuce, wheat, red cabbage and cucumber seeds. The inhibitory effect was partly neutralized by kinetin (20 mg 1−1) and gibberellic acid (50 mg 1−1). The effect of kinetin was more pronounced at 25°C than at 20°C. Substances inhibiting germination were localized in the pericarp of the fruit and were resistant to high temperature.  相似文献   
4.
  1. Birds colliding with turbine rotor blades is a well‐known negative consequence of wind‐power plants. However, there has been far less attention to the risk of birds colliding with the turbine towers, and how to mitigate this risk.
  2. Based on data from the Smøla wind‐power plant in Central Norway, it seems highly likely that willow ptarmigan (the only gallinaceous species found on the island) is prone to collide with turbine towers. By employing a BACI‐approach, we tested if painting the lower parts of turbine towers black would reduce the collision risk.
  3. Overall, there was a 48% reduction in the number of recorded ptarmigan carcasses per search at painted turbines relative to neighboring control (unpainted) ones, with significant variation both within and between years.
  4. Using contrast painting to the turbine towers resulted in significantly reduced number of ptarmigan carcasses found, emphasizing the effectiveness of such a relatively simple mitigation measure.
  相似文献   
5.
Abstract The genes encoding the CryIVB and CryIVD crystal polypeptides of B. thuringiensis subsp. israelensis were cloned indepently on a stable shuttle vector, and transfered into B. sphaericus 2297. Recombinant cells expressed the B. thuringiensis toxins during sporulation and were shown to be toxic to Aedes aegypti fourth instar larvae, whereas the parental strain was not.  相似文献   
6.
7.
Rechargeable graphite dual‐ion batteries (GDIBs) have attracted the attention of electrochemists and material scientists in recent years due to their low cost and high‐performance metrics, such as high power density (≈3–175 kW kg?1), energy efficiency (≈80–90%), long cycling life, and high energy density (up to 200 Wh kg?1), suited for grid‐level stationary storage of electricity. The key feature of GDIBs is the exploitation of the reversible oxidation of the graphite network with concomitant and highly efficient intercalation/deintercalation of bulky anionic species between graphene layers. In this review, historical and current research aspects of GDIBs are discussed, along with key challenges in their development and practical deployment. Specific emphasis is given to the operational mechanism of GDIBs and to unbiased and correct reporting of theoretical cell‐level energy densities.  相似文献   
8.
9.
《Cell》2021,184(25):6081-6100.e26
  1. Download : Download high-res image (148KB)
  2. Download : Download full-size image
  相似文献   
10.
Tau is an intrinsically disordered protein implicated in many neurodegenerative diseases. The repeat domain fragment of tau, tau-K18, is known to undergo a disorder to order transition in the presence of lipid micelles and vesicles, in which helices form in each of the repeat domains. Here, the mechanism of helical structure formation, induced by a phospholipid mimetic, sodium dodecyl sulfate (SDS) at sub-micellar concentrations, has been studied using multiple biophysical probes. A study of the conformational dynamics of the disordered state, using photoinduced electron transfer coupled to fluorescence correlation spectroscopy (PET-FCS) has indicated the presence of an intermediate state, I, in equilibrium with the unfolded state, U. The cooperative binding of the ligand (L), SDS, to I has been shown to induce the formation of a compact, helical intermediate (IL5) within the dead time (∼37 µs) of a continuous flow mixer. Quantitative analysis of the PET-FCS data and the ensemble microsecond kinetic data, suggests that the mechanism of induction of helical structure can be described by a U ↔ I ↔ IL5 ↔ FL5 mechanism, in which the final helical state, FL5, forms from IL5 with a time constant of 50–200 µs. Finally, it has been shown that the helical conformation is an aggregation-competent state that can directly form amyloid fibrils.  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