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   12731篇
  免费   1162篇
  国内免费   1384篇
  2024年   20篇
  2023年   168篇
  2022年   389篇
  2021年   681篇
  2020年   475篇
  2019年   574篇
  2018年   520篇
  2017年   375篇
  2016年   595篇
  2015年   791篇
  2014年   1019篇
  2013年   978篇
  2012年   1199篇
  2011年   1094篇
  2010年   735篇
  2009年   603篇
  2008年   735篇
  2007年   683篇
  2006年   553篇
  2005年   444篇
  2004年   382篇
  2003年   366篇
  2002年   287篇
  2001年   235篇
  2000年   216篇
  1999年   218篇
  1998年   148篇
  1997年   118篇
  1996年   104篇
  1995年   63篇
  1994年   86篇
  1993年   46篇
  1992年   69篇
  1991年   51篇
  1990年   30篇
  1989年   37篇
  1988年   28篇
  1987年   41篇
  1986年   18篇
  1985年   22篇
  1984年   17篇
  1983年   8篇
  1982年   6篇
  1981年   4篇
  1980年   7篇
  1979年   4篇
  1978年   7篇
  1977年   3篇
  1974年   4篇
  1971年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Oresitrophe and Mukdenia (Saxifragaceae) are epilithic sister genera used in traditional Chinese medicine. The taxonomy of Mukdenia, especially of M. acanthifolia, has been controversial. To address this, we produced plastid and mitochondrial data using genome skimming for Mukdenia acanthifolia and Mukdenia rossii, including three individuals of each species. We assembled complete plastomes, mitochondrial CDS and nuclear ribosomal ETS/ITS sequences using these data. Comparative analysis shows that the plastomes of Mukdenia and Oresitrophe are relatively conservative in terms of genome size, structure, gene content, RNA editing sites and codon usage. Five plastid regions that represent hotspots of change (trnH-psbA, psbC-trnS, trnM-atpE, petA-psbJ and ccsA-ndhD) are identified within Mukdenia, and six regions (trnH-psbA, petN-psbM, trnM-atpE, rps16-trnQ, ycf1 and ndhF) contain a higher number of species-specific parsimony-informative sites that may serve as potential DNA barcodes for species identification. To infer phylogenetic relationships between Mukdenia and Oresitrophe, we combined our data with published data based on three different datasets. The monophyly of each species (Oresitrophe rupifraga, M. acanthifolia and M. rossii) and the inferred topology ((M. rossii, M. acanthifolia), O. rupifraga) are well supported in trees reconstructed using the complete plastome sequences, but M. acanthifolia and M. rossii did not form a separate clade in the trees based on ETS + ITS data, while the mitochondrial CDS trees are not well-resolved. We found low recovery of genes in the Angiosperms353 target enrichment panel from our unenriched genome skimming data. Hybridization or incomplete lineage sorting may be the cause of discordance between trees reconstructed from organellar and nuclear data. Considering its morphological distinctiveness and our molecular phylogenetic results, we strongly recommend that M. acanthifolia be treated as a distinct species.  相似文献   
82.
A rapid method for microorganism detection using a piezoelectric quartz crystal sensor (PQC) coated with a thin liquid culture medium film was developed and applied to detect the cell number of Proteus vulgaris. This method employed the viscosity and density response of PQC and utilized the coagulation of gelatine medium solution in which the microorganisms had grown to determine the microorganism indirectly. Three time points (TT1, DT, TT2) were obtained from the coagulation curve and were found to be in good linear relationship with the logarithm of the initial number of P. vulgaris in the range 1·3 × 102−1·3 × 105 cells/ml. The detection was rapid and accurate because the coagulation of the thin liquid culture medium film was quick and the time points in the response curve were sharp and so were easy to determine accurately. The detection time was less than 4 h and only a micro sample was needed. A 5 h preincubation was needed before detection. Some experimental conditions are discussed in detail.  相似文献   
83.
将实验大鼠放置模拟5000m海拔高度低压舱内1、2和4周。结果表明:与对照组比较,1,2和4周组动物的心肌重量分别增加15%,18%和57%;心肌SRCa2+摄取分别降低33%,38%和53%;心肌SRCa2+ATPase活性分别降低54%,60%和74%;钙泵mRNA含量(基因表达分别降低14%,46%和68%。这些结果提示,缺氧导致的SR钙泵功能降低可能是心肌功能受损的重要生化基础之一,而钙泵数目减少可能是钙泵功能降低的分子生物学机制。  相似文献   
84.
通过野生种分离选用的平菇丰收一号,染色体数为9(n=9),菌丝生长速度比一般品种快2—34cm/h,平均投料0.5kg(块)产鲜菇0.6~2.5kg,个别单株重10~20kg左右,生物效率100~150%,高者达200%以上,是一种高产优质、适应性强的新菌种。  相似文献   
85.
朱砂叶螨羧酸脂酶最优测试条件的选择   总被引:1,自引:0,他引:1  
应用二次回归通用旋转组合设计,对朱砂叶螨离体羧酸酯酶测试过程中所需缓冲液pH值、恒温时间、反应温度及底物浓度,设立4因子5水平试验,在考虑4个因子主效应和互作效应的情况下,筛选测试羧酸酯酶的最优条件组合。  相似文献   
86.
本文对准分子激光PRK治疗近视眼息者503例的早期临床结果进行分析,近视范围为-2.0至-15.0D,根据术前屈光度不同分为三组,术后随访三个月.结果证实准分子激光是一种安全、有效、预测性较好的治疗近视眼方法.全部病人提高了裸眼视力,绝大部分保持了最佳矫正视力,且没有产生危及视力的并发症.  相似文献   
87.
本记述了采自西藏小型动物体上的恙螨四新种.隶属恙螨科(Trombiculidae Ewing,1944)的纤恙螨属(Leptotrombitium Nagyio et al,1916)。模式标本保存于军事医学科学院微生物流行病学研究所医学昆虫标本馆,部分副模标本存第一作所在单位。  相似文献   
88.
J M Staub  N Wei    X W Deng 《The Plant cell》1996,8(11):2047-2056
The pleiotropic CONSTITUTIVE PHOTOMORPHOGENIC (COP), DEETIOLATED (DET), and FUSCA (FUS) loci are essential regulatory genes involved in the light control of seedling developmental patterns in Arabidopsis. Although COP1, DET1, COP9, and FUS6 (also called COP11) have been cloned, their biochemical activities and interactions remain elusive. We have recently suggested that multiple pleiotropic COP, DET, and FUS genes may encode subunits of a large regulatory complex. In this study, we generated specific antibodies against Arabidopsis FUS6 and show that accumulation of both COP9 and FUS6 is coordinated in the pleiotropic cop, det, and fus mutant backgrounds and in wild-type plants throughout development. Both COP9 and FUS6 cofractionated into identical high molecular mass fractions in an analytical gel filtration assay, and neither was found in its monomeric form. Moreover, antibodies raised against either COP9 or FUS6 selectively coimmunoprecipitated both proteins. We have also developed an Arabidopsis protoplast immunolocalization assay and demonstrated that the COP9 complex is localized in the nucleus and that its nuclear localization is not affected by light conditions or tissue types. The integrated genetic and biochemical results strongly support the conclusion that both COP9 and FUS6 are components of the nuclear-localized COP9 complex. Therefore, we have provided the strongest evidence for the conclusion that at least some of the pleiotropic COP, DET, and FUS loci act in the same signaling pathway.  相似文献   
89.
云南普通马矮型马蛋白多态性及其品种分化关系   总被引:3,自引:1,他引:2  
宿兵  解德文 《动物学研究》1995,16(2):126-131
本文运用蛋白电泳技术对来自云南省文山州马关县和麻栗坡县的21匹普通马和14匹矮型马进行了分析。共分析遗传座位44个,其中有10个座位检测到多态性。根据分子钟假说和相应的公式,推算两者的分歧时间约为18.5万年。  相似文献   
90.
发情期小灵猫行为的研究   总被引:9,自引:0,他引:9  
徐宏发  朱兵 《动物学研究》1995,16(4):359-364
本文对笼养小灵猫发情期的繁殖行为进行了观察。结果表明:小灵猫一年有两次发情期,绝大部分的小灵猫在春季(2-4月)发情,少数个体在秋季(8月底至9月)出现第2次发情。发情期雄性小灵猫频繁地发出求偶叫声和增加擦香次数。雄猫的擦香行为和求偶叫声可促使雌猫的发情,发情期一系列性行为对雌雄交配的成功与否有重要的意义。  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