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   48181篇
  免费   3657篇
  国内免费   3482篇
  55320篇
  2024年   120篇
  2023年   577篇
  2022年   1375篇
  2021年   2226篇
  2020年   1519篇
  2019年   1922篇
  2018年   2050篇
  2017年   1677篇
  2016年   2173篇
  2015年   2506篇
  2014年   3218篇
  2013年   3480篇
  2012年   3965篇
  2011年   3707篇
  2010年   2622篇
  2009年   2299篇
  2008年   2631篇
  2007年   2363篇
  2006年   2067篇
  2005年   1698篇
  2004年   1595篇
  2003年   1503篇
  2002年   1225篇
  2001年   1000篇
  2000年   839篇
  1999年   614篇
  1998年   381篇
  1997年   318篇
  1996年   306篇
  1995年   318篇
  1994年   291篇
  1993年   225篇
  1992年   290篇
  1991年   259篇
  1990年   208篇
  1989年   192篇
  1988年   129篇
  1987年   175篇
  1986年   145篇
  1985年   128篇
  1984年   101篇
  1983年   95篇
  1982年   82篇
  1981年   78篇
  1980年   52篇
  1979年   62篇
  1978年   66篇
  1976年   51篇
  1973年   63篇
  1972年   52篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Soluble microbial products (SMPs) are considered as the main organic components in wastewater treatment plant effluent from biological wastewater treatment systems. To investigate and explore SMP metabolism pathway for further treatment and control, two innovative mechanistically based activated sludge models were developed by extension of activated sludge model no.3 (ASM3). One was the model by combining SMP formation and degradation (ASM3-SMP model) processes with ASM3, and the other by combining both SMP and simultaneous substrate storage and growth (SSSG) mechanisms with ASM3 (SSSG-ASM3-SMP model). The detailed schematic modification and process supplements were introduced for comprehensively understanding all the mechanisms involved in the activated sludge process. The evaluations of these two models were demonstrated by a laboratory-scale sequencing batch reactor (SBR) operated under aerated/non-aerated conditions. The simulated and measured results indicated that SMP comprised about 83% of total soluble chemical oxygen demand (SCOD) in which biomass-associated products (BAPs) were predominant compared with utilization-associated products (UAPs). It also elucidated that there should be a minimum SMP value as the reactive time increases continuously and this conclusion could be used to optimize effluent SCOD in activated sludge processes. The comparative results among ASM3, ASM3-SMP and SSSG-ASM3-SMP models and the experimental measurements (SCOD, ammonia and nitrate nitrogen) showed clearly the best agreement with SSSG-ASM3-SMP simulation values (R = 0.993), strongly suggesting that both SMP formation and degradation and SSSG mechanisms are necessary in biologically activated sludge modeling for municipal wastewater treatment.  相似文献   
82.
Controllable storage and release of solar energy has always been a highlighted scientific issue for its benefit of mankind. Solar thermal fuels (STFs) supply a closed cycle and renewable energy‐storage strategy by transforming solar energy into chemical energy stored in the conformation of molecular isomers, such as cis/trans‐azobenzene, and releasing it as heat under various stimuli. Although the potential high energy density of the STFs which are based on the hybrids of azobenzene derivatives and carbon nanomaterials has been reported the solvent‐assistant charging hinders their practicability. In this study, a solid‐state STF device is designed and fabricated by compositing one photoliquefiable azobenzene (PLAZ) derivative with a flexible fabric template. The photoinduced phase transition of the PLAZ derivative enables the charging of the flexible STFs to be totally solvent‐free. Interestingly, the energy‐storage capacity (energy density ≈201 J g?1) of flexible PLAZ STFs has been improved by the soft fabric template. The exothermic situation is monitored with one infrared camera, which shows 4 °C temperature difference between charged and discharged samples under blue light stimulus. The flexible STFs are may be used in practice as heating equipment.  相似文献   
83.
日本绒螯蟹血淋巴细胞的研究   总被引:1,自引:0,他引:1  
周玉 《水生生物学报》2003,27(6):664-666
甲壳动物血淋巴细胞具有吞噬异物的功能,其种类、数量与其免疫功能密切相关。    相似文献   
84.
85.
Almost all infectious diseases are initiated at mucosal surfaces, yet intramuscular or subcutaneous vaccination usually provides only minimal protection at sites of infection owing to suboptimal activation of the mucosal immune system. The neonatal Fc receptor (FcRn) mediates the transport of IgG across polarized epithelial cells lining mucosal surfaces. We mimicked this process by fusing a model antigen, herpes simplex virus type-2 (HSV-2) glycoprotein gD, to an IgG Fc fragment. Intranasal immunization, together with the adjuvant CpG, completely protected wild-type, but not FcRn knockout, mice after intravaginal challenge with virulent HSV-2 186. This immunization strategy induced efficient mucosal and systemic antibody, B- and T-cell immune responses, with stable protection for at least 6 months after vaccination in most of the immunized animals. The FcRn-IgG transcellular transport pathway may provide a general delivery route for subunit vaccines against many mucosal pathogens.  相似文献   
86.
The features of reproductive biology of rose plants from the sections Caninae Crep., Indocae Thory, Cinnamomae DC., Synstylae DC. were studied by cytological methods and with the help of scanning electron microscopy for many years. The results obtained are reported.  相似文献   
87.
Immunoprecipitation of Na,K-ATPase from kidney homogenate by antibodies against alpha1-subunit results in the precipitation of several proteins together with the Na,K-ATPase. A protein with molecular mass of about 67 kD interacting with antibodies against melittin (melittin-like protein, MLP) was found in the precipitate when immunoprecipitation was done in the presence of ouabain. If immunoprecipitation was done using antibodies against melittin, MLP and Na,K-ATPase alpha1-subunit were detected in the precipitate, and the amount of alpha1-subunit in the precipitate was increased after the addition of ouabain to the immunoprecipitation medium. MLP was purified from mouse kidney homogenate using immunoaffinity chromatography with antibodies against melittin. The addition of MLP to purified FITC-labeled Na,K-ATPase decreases fluorescence in medium with K+ and increases it in medium with Na+. The enhancement of fluorescence depends upon the MLP concentration. The N-terminal sequence of MLP determined by the Edman method is the following: HPPKRVRSRLNG. No proteins with such N-terminal sequence were found in the protein sequence databases. However, we revealed five amino acid sequences that contain this peptide in the middle part of the chain at distance 553 amino acids from the C-terminus (that corresponds to protein with molecular mass of about 67 kD). Analysis of amino acid sequence located between C-terminus and HPPKRVRSRLNG in all found sequences has shown that they were highly conservative and include WD40 repeats. It is suggested that the 67-kD MLP either belongs to the found protein family or was a product of proteolysis of one of them.  相似文献   
88.
89.
90.
Our earlier studies on cell adhesion to immobilized carbohydrates are extended here to a marine bacterium, Vibrio furnissii. Apparently one lectin mediates the binding of these cells to glycosides of N-acetylglucosamine, mannose, and glucose covalently linked to Agarose beads. Kinetic studies show that protein synthesis is required for initiating and for maintaining adhesion to the glycosides. Furthermore, a pro- mutant binds to GlcNAc-beads at Pro concentrations insufficient to support cell growth. Expression of the functional lectin therefore predominates under conditions of limiting protein synthesis. Thus, cells adhere to the sugars in an environment compatible with protein synthesis, and deadhere when depleted of any required nutrient, presumably to migrate to a more favorable locale. The adhesion-deadhesion apparatus thereby permits constant monitoring of the surrounding environment, comprising a "nutrient sensorium".  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