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   2285篇
  免费   94篇
  国内免费   9篇
化学   1882篇
晶体学   18篇
力学   28篇
数学   70篇
物理学   390篇
  2023年   8篇
  2022年   8篇
  2021年   24篇
  2020年   34篇
  2019年   36篇
  2018年   31篇
  2017年   23篇
  2016年   56篇
  2015年   49篇
  2014年   58篇
  2013年   91篇
  2012年   114篇
  2011年   184篇
  2010年   78篇
  2009年   95篇
  2008年   181篇
  2007年   160篇
  2006年   154篇
  2005年   144篇
  2004年   133篇
  2003年   120篇
  2002年   100篇
  2001年   24篇
  2000年   37篇
  1999年   32篇
  1998年   26篇
  1997年   28篇
  1996年   28篇
  1995年   16篇
  1994年   22篇
  1993年   18篇
  1992年   18篇
  1991年   12篇
  1990年   15篇
  1989年   10篇
  1988年   10篇
  1987年   13篇
  1985年   19篇
  1984年   26篇
  1983年   12篇
  1982年   24篇
  1981年   18篇
  1980年   8篇
  1979年   12篇
  1978年   9篇
  1977年   7篇
  1976年   8篇
  1975年   10篇
  1974年   5篇
  1973年   16篇
排序方式: 共有2388条查询结果,搜索用时 15 毫秒
111.

We investigate a hidden-variable theory introduced by Kochen and Specker. The “hidden” results of measurements are either 1 or − 1. We suppose the validity of Sum rule and Product rule. Kochen and Specker suppose the two operations Sum rule and Product rule commute with each other. It is shown that the two operations Sum rule and Product rule do not commute with each other when we want to avoid the Kochen and Specker paradox. Otherwise we encounter the Kochen and Specker paradox. We mention the supposition for Greenberger, Horne, and Zeilinger paradox. It is discussed that only Product rule is necessary for the paradox. We give up the two paradoxes if (1) Sum rule and Product rule do not commute with each other and (2) Product rule is not valid.

  相似文献   
112.
113.
The total synthesis of 7,10‐epimer of the proposed structure of amphidinolide N was accomplished. The requisite chiral C17–C29 subunit was assembled stereoselectively via Keck allylation, Shi epoxidation, diastereoselective 1,3‐reduction, and a later oxidative synthesis of the THF framework. The C1–C13 and C17–C29 subunits were successfully coupled using a Enders RAMP “linchpin” as the C14–C16 three carbon unit, thereby controlling the chirality at C14 and C16. The labile allyl epoxy moiety was successfully constructed by Grieco–Nishizawa olefination at a final stage of the synthesis.  相似文献   
114.
115.

Abstract  

Droplets impinging on a hot surface that is near the Leidenfrost temperature were experimentally investigated. Ejection of jets from the top of the droplet was observed during the transient interaction between the droplet and a hot wall. We term this phenomenon jet ejection from droplets. When the bottom of the droplet initially impacts the hot surface, a jet is to be ejected from the top of the droplet. The jet ejection occurred only at low impact velocities and around the wetting limit temperature. It was not observed when droplets were dropped from large heights or when the surface was at a high temperature.  相似文献   
116.
117.
Abstract

1,4-Bis(p-tert-butylphenylselenomethyl) benzene was synthesized, and used as a bifunctional photoiniferter for the polymerization of styrene. Both the polymer yields and the number average of molecular weights (n) of polymers increased with the polymerization. The polymerization of styrene by this iniferter permitted telechelic polystyrene containing arylseleno groups at both chain ends, and the degree of functionality was 1.9. The seleno groups of both chain ends of polystyrene were reduced quantitatively by tri-n-butyltin hydride. These seleno groups in polystyrene were also eliminated by treatment with hydrogen peroxide to give telechelic polystyrene with carbon-carbon double bond at both chain ends. Further, polystyrene with double bonds was converted to telechelic polystyrene carrying terminal functional groups as epoxy, hydroxy, and iodide group, respectively.

  相似文献   
118.
Abstract

The authors have developed a novel, rapid, convenient, and specific gene detection method, named the ‘DNA sensor,’ using a graphite electrode loaded with DNA probes. Synthesized oligonucleotide (5-TGCAGTTCCGGTGGCTGATC-3′) complementary to oncogene v-myc was employed for a model probe. The oligonucleotide was chemically adsorbed on a basal plane pyrolytic graphite (BPPG) electrode. The sensor was able to be applied to a hybridization reaction (40°C) in a linearized pVM623 solution carrying the Pst I fragment of v-myc (1.5 kbp).

After the hybridization reaction, the sensor was immersed into an acridine orange solution (1 μM) and washed with a phosphate buffer (pH 7.0). Acridine orange intercalated between base pairs of the formed double stranded DNAs on the electrode. The anodic peak potential of acridine orange that interacted with the DNAs on the electrode was measured. The positive shift of the peak potential increased in proportional to the pVM623 concentration in the hybridization reaction. 10?1 g/ml of pVM623 was able to be detected in the buffer solution using the sensor. This gene detection was completed within an hour.  相似文献   
119.
Highlights? ActVA-ORF5 is a flavin-dependent monooxygenase required for actinorhodin biosynthesis ? ActVA-ORF5 and its three close homologs were functionally dissected ? ActVA-ORF5 and Gra-21 are bifunctional at C-6/C-8, while Med-7 acts only for C-6 ? AlnT exhibits different regiospecificity for oxidation of tricyclic substrates  相似文献   
120.
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