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   3911篇
  免费   112篇
  国内免费   10篇
化学   2273篇
晶体学   60篇
力学   57篇
数学   633篇
物理学   1010篇
  2020年   44篇
  2019年   51篇
  2018年   39篇
  2017年   32篇
  2016年   77篇
  2015年   72篇
  2014年   73篇
  2013年   148篇
  2012年   139篇
  2011年   138篇
  2010年   113篇
  2009年   91篇
  2008年   131篇
  2007年   109篇
  2006年   116篇
  2005年   116篇
  2004年   106篇
  2003年   83篇
  2002年   98篇
  2001年   70篇
  2000年   96篇
  1999年   78篇
  1998年   57篇
  1997年   63篇
  1996年   67篇
  1995年   59篇
  1994年   79篇
  1993年   77篇
  1992年   64篇
  1991年   57篇
  1990年   57篇
  1989年   43篇
  1988年   40篇
  1987年   48篇
  1986年   60篇
  1985年   62篇
  1984年   56篇
  1983年   55篇
  1982年   50篇
  1981年   43篇
  1980年   69篇
  1979年   48篇
  1978年   60篇
  1977年   61篇
  1976年   60篇
  1975年   60篇
  1974年   48篇
  1973年   55篇
  1972年   35篇
  1971年   33篇
排序方式: 共有4033条查询结果,搜索用时 15 毫秒
181.
Mono-and bis-donor-acceptor formation (donor=AH3, Y = N, P, As, Sb, Bi and AH2, O, S, Se, Te) is discussed on the basis of quantum chemical (ab initio) calculations for π-bonded low-coordinated phosphorus cations, evaluating new types of bis-donor adducts.  相似文献   
182.
We formally derive and rigorously justify the modulation equations of lowest order for the interaction of two modulated pulses on a one-dimensional nonlinear oscillator chain. We show that solutions with the initial form of the assumed ansatz preserve this form over time intervals with positive macroscopic length, and we show a bound on the possible shift of the envelope caused by the interaction. Thus, we rigorously justify and quantify the statement that under the given conditions there is almost no interaction of the modulated pulses.  相似文献   
183.
184.
185.
In the original traveling salesman problem, the traveling salesman has the task to find the shortest closed tour through a proposed set of nodes, touching each node exactly once and returning to the initial node at the end. For the sake of the tour length to be minimized, nodes close to each other might not be visited one after the other but separated in the tour. However, for some practical applications, it is useful to group nodes to clusters, such that all nodes of a cluster are visited contiguously. Here we present an approach which leads to an automatic clustering with a clustering parameter governing the sizes of the clusters.  相似文献   
186.
Abstract

RP groups are useful cluster constituents: They warrant a detailed analysis of cluster reactions even in those cases where metal-metal bonds break and where, without these linking groups, the clusters would desintegrate.  相似文献   
187.
188.
An optimum nanoprecipitation technique for gelatin nanoparticles is established, based on aqueous gelatin solution and ethanolic solution containing stabilizer. Crosslinking with glutaraldehyde results in stable gelatine nanoparticles. Several factors such as the surfactant concentration, type of surfactant, type of nonsolvent and gelatin concentration are evaluated. Gelatin nanoparticles with 200–300 nm can be produced using 20–30 mg mL?1 of gelatin and a minimum of 7% w/v stabilizer (Poloxamer 407 or 188). Furthermore, methanol and ethanol are good nonsolvents, whereas other nonsolvents such as acetone, isopropyl alcohol, and acetonitrile, result in phase separation and visible precipitates. The entrapment efficiency of fluorescein‐isothiocyanate (FITC)‐dextran as model drug was determined to 50% with no substantial effect on particle size. 80% of the drug is only released after enzymatic digestion.

  相似文献   

189.
Enzyme immunoassays with optical detection are amongst the most widely used bioanalytical tools. We defined seven parameters for the quality assessment of immunoassays that were addressed in a systematic study of direct and indirect immunoassays, using the enzymes horseradish peroxidase (HRP) and alkaline phosphatase (AP), the chromogenic substrates 3,3′,5,5′-tetramethylbenzidine (TMB) and para-nitrophenyl phosphate, and the fluorescent substrates 3-(4-hydroxyphenyl)propionic acid and 4-methylumbelliferyl phosphate. The same monoclonal antibody against caffeine was used throughout the study. The four quality parameters regarding the standard curve were the test midpoint (sensitivity), the measurement range, the relative dynamic range of the signal, and the goodness of fit of the adjusted four-parameter logistic function. All HRP immunoassays showed a higher sensitivity compared to the AP assays. On the basis of all four criteria, it was established that the direct assay format is superior to the indirect format, the immunoassay using HRP TMB fulfilling all requirements best. In a second step, caffeine concentrations in 24 beverage and cosmetics samples were determined and three more quality parameters were assessed with this application. The direct HRP TMB assay showed one of the best intra- and inter-plate precisions and the best accuracy, defined by the correlation of results with those from the chosen reference method liquid chromatography tandem mass spectrometry (LC-MS/MS). Considering all criteria, HRP TMB seems to be the enzyme substrate system of choice preferably used in the direct assay format.
Figure
Overview on the different enzyme immunoassay formats compared  相似文献   
190.
[首页] « 上一页 [14] [15] [16] [17] [18] 19 [20] [21] [22] [23] [24] 下一页 » 末  页»
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