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   1033篇
  免费   84篇
  国内免费   66篇
  2024年   4篇
  2023年   16篇
  2022年   30篇
  2021年   80篇
  2020年   38篇
  2019年   52篇
  2018年   48篇
  2017年   35篇
  2016年   53篇
  2015年   70篇
  2014年   79篇
  2013年   73篇
  2012年   109篇
  2011年   96篇
  2010年   47篇
  2009年   38篇
  2008年   52篇
  2007年   41篇
  2006年   34篇
  2005年   28篇
  2004年   29篇
  2003年   22篇
  2002年   12篇
  2001年   9篇
  2000年   11篇
  1999年   14篇
  1998年   7篇
  1997年   8篇
  1996年   3篇
  1995年   4篇
  1994年   6篇
  1993年   6篇
  1992年   8篇
  1991年   8篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1986年   3篇
  1985年   2篇
  1983年   1篇
  1982年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有1183条查询结果,搜索用时 78 毫秒
991.
Abstract Gas chromatographic and mass spectral analyses were conducted on the pheromone gland extracts of female moth of Helicoverpa armigera (Lepidoptera:Noctuidae). Saturated aldehyde (16:Ald), (Z)-9-hexadecenal (Z-9–16:Ald), (Z)-11-hexadecenal (Z-11–16:Ald), hexade-canol (16:OH) and (Z)-11-hexadecenol (2–11–16:OH) were found from gland extracts in the ratio of 6.1:4. 5 :100:3. 5 :8.8. In field tests of Shandong and Shanxi Provinces, 2 mg blends of Z -11–16:Ald and Z-9–16:Ald (97:3) applied on a rubber dispenser effectively attracted H. armigera males. The addition of 4%-7% 16 :Ald to the binary mixture caused increase over that of the binary mixture. The addition of 1%Z-11–16:OH to binary or trinary mixture may reduce catches, while addition of 5% Z-11–16:OH reduced catches singnificantly.  相似文献   
992.
大鼠腓肠肌在10Hz电刺激持续收缩运动中,肌细胞膜电位表现为静息电位(RP)和复合动作电位(CAP)幅值呈下降的趋势,且CAP的时程展宽。经过9周的游泳训练后,训练组动物整体的运动耐力明显提高;在相同的持续收缩运动时间内,训练组的RP和CAP的下降幅度明显小于对照组(P<0.05);并发现训练组NAa ̄+,K ̄+-ATP酶活性明显提高(P<0.01)。结果提示,体力训练使肌细胞膜的功能产生了适应性变化,提高了对运动的耐受能力。  相似文献   
993.
Nitric oxide myoglobin (MbNO) at 300 K was photodissociated with 405 nm pulses. The NO recombination in several mutants of iron and cobalt myoglobins was investigated at a time resolution of ca. 70 fs. The geminate recombination of NO was nonexponential on sub-nanosecond time scales. For both metals, the change of the detailed structure of the heme pocket (position 68 mutations) caused significant changes in the rates of recombination; however, the metal substitution influenced the recombination much less than did amino acid substitution. The results indicate a primary role of the heme pocket structure in the dynamics, and they suggest that proximal protein relaxation is not the limiting factor in the geminate recombination process. Recombination in cobalt derivatives is somewhat more efficient on the sub-nanosecond time scales than in corresponding iron myoglobins, consistent with other results that show a greater intrinsic reactivity toward the NO of cobalt compared with the iron heme. A comparison of results using Soret band excitation with previous Q-state excitation studies demonstrates that the ligand dissociates with a similar kinetic energy in both cases, suggesting fast intramolecular energy redistribution before dissociation.  相似文献   
994.
995.
Supercapacitor (SC) is one of the most promising electrochemical energy-storage devices. However, the practical application of SCs is limited by the low-energy density. Herein, high-temperature shock (HTS)-derived ultrafine structure-activated porous carbon (UAPC) with N, O functional groups is reported as high-energy density SCs carbon. The process of ultrafast joule heating and cooling effectively transfers general-purposed carbon into electrochemical-activated carbon. The UAPC-based SCs exhibit an energy density of up to 129 Wh kg−1 in EMIMBF4 ionic liquid, which outperform almost all reported and commercial SCs (22 Wh kg−1). The outstanding electrochemical performance of UAPC is attributed to the ultrafine structure and N, O functional groups, which enlarges the surface area, improves the surface wettability of UAPC electrodes, and provides pseudocapacitance. The facile and efficient ultrafast-processing strategy has opened up an unprecedented pathway for the application of low-value carbon for the electrode design and application of SCs.  相似文献   
996.
Deoxyhypusine formation on the 18 kDa eIF-4D precursor is due to a covalent linkage between a lysine residue of the protein and the aminobutyl moiety derived from spermidine. The deoxyhypusine is then hydroxylated to form hypusine. This post-translational modification represents one of the most specific spermidine-dependent biochemical events in eukaryotic cells. Deoxyhypusine formation can be performed in vitro at pH 9.5 and is greatly stimulated by NAD+. Using the labeling of the 18 kDa protein by [3H]spermidine as an assay for deoxyhypusine formation, we found that (i) significant deoxyhypusine formation can be demonstrated in vitro at pH 7.2 only if NAD+ is present, (ii) deoxyhypusine formation was sensitive to buffer composition; buffers made of basic amino acids and Tris were inhibitory, (iii) sulfhydryl reagents and metal ions such as Cu2+ and Fe3+ were potent inhibitors of deoxyhypusine formation and (iv) the 18 kDa protein substrate was heat-stable. The in vitro activity of deoxyhypusine formation, which depends on the presence of both enzyme and protein substrate, can be separated from the product, eIF-4D, by a one-step Cibacron blue dye affinity column. Taking advantage of this finding, we have developed a simple procedure, based on the use of Cibacron blue dye, for partially purifying both the deoxyhypusine-forming enzyme and the 18 kDa protein substrate. When the partially purified enzyme and protein substrate were mixed in the presence of 1 mM NAD+ and [3H]spermidine, the 18 kDa protein was radiolabeled, no labeling could be detected if any one component was absent. Using partially purified enzyme, we have also determined the half-life of the protein substrate in alpha-difluoromethyl ornithine (DFMO)-treated NB-15 cells and found it to be longer than 10 h.  相似文献   
997.
为揭示遗传改良对主要造林用材树种叶和种实性状的影响,阐明性状的变异趋势,该研究以杉木第4轮育种的精选树(改良群体)、四省五地的表型优树与古树(未改良群体)为对象,调查了218个无性系的针叶和种实性状指标,采用方差分析和多重对比方法研究遗传改良对杉木及不同类型杉木的表型差异,并通过相关性分析探究遗传改良对杉木针叶和球果部分表型性状的影响,以及利用主成分分析和聚类分析进行了分类。结果表明:(1)未改良群体的针叶长、针叶宽和出籽率分别比改良群体小13.28%、10.81%和33.90%,其他性状表现为未改良群体大于改良群体,差异在10.90%~27.03%之间。未改良群体球果长、球果宽和出籽率的变异系数,分别比改良群体大9.14%、12.73%和15.38%。(2)球果长、球果宽、苞鳞长和苞鳞宽4个性状,在未改良群体中仅有球果长和球果宽(0.931)、苞鳞长和苞鳞宽(0.622)之间呈极显著正相关,经遗传改良后,该4个性状两两之间均呈显著或极显著正相关。(3)四川雅安(SCYA)的球果长和球果宽的性状比改良群体大48.83%和53.26%,安徽黄山(AHHS)的百粒重比改良群体大16.92%。(4)遗传改良导致松张型球果的杉木比例降低,紧包型和反翘型球果的杉木比例增加。综上认为,杉木的遗传改良导致球果大小下降,改变了不同针叶和球果类型的比例,同时会改变针叶性状和种实性状的相关性,将为杉木种质资源评价和未来多目标育种提供依据。  相似文献   
998.
<正>Dear Editor,The peste des petits ruminants virus(PPRV)causes an increasingly important viral disease of livestock that predominantly infects small ruminants such as goats and sheep.It belongs to the Paramyxoviridae family and is classified as the fourth member of the genus Morbillivirus because of its genetic similarity with other members of this genus,which includes measles virus(MV),rinderpest virus(RPV),canine distemper virus  相似文献   
999.
The west Jilin Province is a typical area in the ecotone between agriculture and animal husbandry, with a frangible eco-environment. With respect to the three aspects of water resource, natural disasters and land degradation, 10 indices were selected to establish a mat-ter-element model for the assessment of eco-envir-onmental frangibility in the west Jilin Province. The results indicate that during 1985-2000, Qian'an, Fuyu, and Changling had the least frangibility (level I), followed by Da'an and Qianguo (level II), and Taobei, Zhenlai, Taonan, and Tongyu had the highest frangibility (level III). On the whole, the counties in Songyuan city were less frangible than those in Baicheng city. Different counties had different frangibilities to environmental factors, e.g., Da'an and Tongyu were frangible in water resource con-ditions; Taobei, Zhenlai, Taonan, Tongyu and Qian'an suffered most from natural disasters; while Taobei, Taonan and Qianguo were threatened by severe land degradation.  相似文献   
1000.
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