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   24474篇
  免费   2113篇
  国内免费   1130篇
  27717篇
  2024年   49篇
  2023年   216篇
  2022年   595篇
  2021年   1049篇
  2020年   605篇
  2019年   772篇
  2018年   834篇
  2017年   699篇
  2016年   888篇
  2015年   1394篇
  2014年   1613篇
  2013年   1865篇
  2012年   2248篇
  2011年   2075篇
  2010年   1304篇
  2009年   1209篇
  2008年   1365篇
  2007年   1243篇
  2006年   1176篇
  2005年   987篇
  2004年   946篇
  2003年   718篇
  2002年   723篇
  2001年   425篇
  2000年   341篇
  1999年   350篇
  1998年   269篇
  1997年   183篇
  1996年   176篇
  1995年   159篇
  1994年   173篇
  1993年   121篇
  1992年   142篇
  1991年   102篇
  1990年   98篇
  1989年   97篇
  1988年   89篇
  1987年   58篇
  1986年   61篇
  1985年   42篇
  1984年   46篇
  1983年   36篇
  1982年   30篇
  1981年   20篇
  1980年   13篇
  1979年   14篇
  1977年   11篇
  1975年   10篇
  1974年   20篇
  1973年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The garnet-type phase Li7La3Zr2O12 (LLZO) attracts significant attention as an oxide solid electrolyte to enable safe and robust solid-state batteries (SSBs) with potentially high energy density. However, while significant progress has been made in demonstrating compatibility with Li metal, integrating LLZO into composite cathodes remains a challenge. The current perspective focuses on the critical issues that need to be addressed to achieve the ultimate goal of an all-solid-state LLZO-based battery that delivers safety, durability, and pack-level performance characteristics that are unobtainable with state-of-the-art Li-ion batteries. This perspective complements existing reviews of solid/solid interfaces with more emphasis on understanding numerous homo- and heteroionic interfaces in a pure oxide-based SSB and the various phenomena that accompany the evolution of the chemical, electrochemical, structural, morphological, and mechanical properties of those interfaces during processing and operation. Finally, the insights gained from a comprehensive literature survey of LLZO–cathode interfaces are used to guide efforts for the development of LLZO-based SSBs.  相似文献   
52.
A series of plasmids were constructed to examine the effects of p19 and orf1‐orf2 genes from Bacillus thuringiensis on Cyt1Aa synthesis and inclusion formation. The plasmids expressed the cyt1Aa gene along with either p19 or orf1‐orf2, or each of them coordinatively with p20 in the acrystalliferous strain of B. thuringiensis subsp. israelensis 4Q7. No effect on the expression of Cyt1Aa protein was found when P19 or Orf1‐Orf2 co‐expressed with Cyt1Aa. However, when including p20 gene, the constructs with p19 or orf1‐orf2 gene produced lower yield of Cyt1Aa proteins than without p19 or orf1‐orf2 gene. Electron microscopy observation and bioassay showed that P19 and Orf1‐Orf2 have no influence on the crystal size and toxicity of Cyt1Aa protein. It is presumed that P19 and Orf1‐Orf2 might have negative effects on Cyt1Aa synthesis in B. thuringiensis.  相似文献   
53.
A brachiopod fauna including 19 species of 17 genera from an exotic block in the Indus–Tsangpo suture zone in southern Tibet is described and illustrated. The brachiopod fauna is dominated by Martinia elegans and two new taxa: Jinomarginifera lhazeensis gen. et sp. nov. and Zhejiangospirifer giganteus sp. nov. The fauna is closely comparable with those from the middle and upper parts of the Wargal Formation and the Chhidru Formation in the Salt Range of Pakistan, the Chitichun Limestone in southern Tibet, and the Basleo area of West Timor, and these correlations suggest a Wuchiapingian age. The fauna exhibits substantial links with both peri–Gondwanan and Cathaysian faunas, which may imply that it is a seamount biota originally located in the southern margin of the Neotethys during the Late Permian, and was later (in the early Cenozoic) displaced and became sandwiched into younger marine deposits in the collision process between India and Eurasia.  相似文献   
54.
尿素氮-葡萄糖双功能分析仪的研究   总被引:2,自引:0,他引:2  
由固定化脲酶、谷氨酸脱氢酶、谷氨酸氧化酶、葡萄糖氧化酶的复合酶膜组成的双电极系统,可以同时测定尿素氮和葡萄糖的含量,每次进样量为25μl,20s即可测定出尿素氮和葡萄糖的含量。在0~60mg/dl尿素氮、0~500mg/dl葡萄糖范围内具有良好的线性关系。连续测定20次的变异系数分别为1.02%和1.05%。酶膜使用寿命为两星期以上。此仪器可广泛应用于临床检验和体育训练中。  相似文献   
55.
高压静电场处理沙棘插条生根状况的初步研究   总被引:2,自引:0,他引:2  
用高压静电场处理沙棘插条研究生根状况,方法简便易于处理,该装置适于进行大规模的处理,从目前研究表明:高压静电场对沙棘插条有正刺激效应,并以电场强度为3.9kv/cm,时间为40分钟处理最佳。  相似文献   
56.
低能量He—Ne激光血管内照射治疗银屑病21例报告   总被引:1,自引:0,他引:1  
21例寻常型银屑病患者,经用He-Ne激光血管内照射,功率3.5-5mw,每日照射一次,每次1小时,10次一疗程,同时伴用vitc2givq.d及鼻吸氧,二疗程间休息4-7天,经5-35次治疗,近期疗效:近期痊愈5例(23.81%),显效6例(28.57%),好转10例(47.62%),总有效率100%,复发1例(4.76%)。  相似文献   
57.
Treatment of cultured bovine carotid artery endothelial cells with 0.1 µM human plasmin has been reported to induce a receptor-mediated short burst of arachidonate release, which is a pertussis toxin-sensitive and extracellular calcium-dependent reaction. Plasmin-induced calcium influx in cells was significantly inhibited by pretreatment with pertussis toxin, indicating that the former was coupled with a pertussis toxin-sensitive guanosine 5-triphosphate (GTP)-binding protein. Plasmin significantly induced the formation of lysophosphatidylcholine but not lysophosphatidylethanolamine. A cellular phospholipase A2 with an arachidonyl specificity at the sn-2 position of phosphatidylcholine, which required submicromolar calcium, was identified as a cytosolic phospholipase A2 by immunoblot analysis. By a cell-free enzyme activity assay and immunoblot analysis, plasmin was found to induce a translocation of the cytosolic phospholipase A2 from the cytosol to the membrane. Taken together, the results suggest that plasmin bound to its putative receptor and activated a GTP-binding protein coupled to calcium influx channel, followed by translocation and activation of cytosolic phospholipase A2 in endothelial cells.  相似文献   
58.
Intraspecific variation of four agamospecies ofHieracium sect.Alpina was studied using RAPD and isozyme techniques. No variation in either multiprimer RAPD or multi-enzyme phenotypes was observed withinH. holosericeum, suggesting that this widespread species consists of only a single genotype. A low level of within-population isozyme variation was seen inH. tenuifrons andH. calenduliflorum, the origin of which appears to be consistent with somatic mutation. Most isozyme and all RAPD variation in these two species was partitioned between populations. A strong correlation with geography suggests that its cause may be due to polytopic (-polyphyletic?) origin or perhaps to mutation and dispersal. The most variable species wasH. alpinum, in which isozyme variation occurred mostly within populations rather than between them, suggesting occasional sexual events or that the parents ofH. alpinum were heterozygous. RAPD variation in this species, in contrast, was partitioned between Scottish and Swiss populations, suggesting the existence of geographical races.  相似文献   
59.
The fluid dynamics of sperm motility near both rigid and elastic walls is studied using the immersed boundary method. Simulations of both single and interacting organisms are presented. In particular, we find that nearby organisms originally undulating with a 90° phase shift may adjust their relative swimming velocities and phase-lock. Comparisons with previous analytical results are also discussed. The tendency of a near-wall to attract organisms is demonstrated.  相似文献   
60.
Aphelenchoides resinosi n. sp. and Ektaphelenchus joyceae n. sp. are described and illustrated from red pines of the Allegheny plateau of Maryland, USA. The new species were found in trees infested with Bursaphelenchus xylophilus. Primary diagnostic characters of A. resinosi females are constriction of the head, basal stylet knobs, tong postuterine sac, two incisures in the lateral field, and conical tail four to five anal body widths long with a simple terminal mucro. Diagnostic characters of the males are two pairs of subventral caudal papillae and spicule shape: Primary diagnostic characters of E. joyceae females are a slight constriction of the head, six similar lips, conical tail, and short postuterine sac. Diagnostic characters of the males are spicule size and shape, a single row of spermatocytes, and one pair of caudal papillae. Within-tree distributions of A. resinosi and E. joyceae are presented. A total of 70% of both red-needled and chlorotic-needled trees in the study were positive for A. resinosi and E. joyceae. Branch hierarchy was related to the percentage of samples positive for A. resinosi.  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