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   6131篇
  免费   164篇
  国内免费   19篇
化学   4486篇
晶体学   70篇
力学   75篇
综合类   1篇
数学   254篇
物理学   1428篇
  2022年   27篇
  2021年   68篇
  2020年   82篇
  2019年   78篇
  2018年   55篇
  2017年   46篇
  2016年   95篇
  2015年   101篇
  2014年   109篇
  2013年   257篇
  2012年   256篇
  2011年   323篇
  2010年   154篇
  2009年   165篇
  2008年   311篇
  2007年   310篇
  2006年   316篇
  2005年   319篇
  2004年   315篇
  2003年   222篇
  2002年   217篇
  2001年   195篇
  2000年   180篇
  1999年   103篇
  1998年   51篇
  1997年   66篇
  1996年   90篇
  1995年   70篇
  1994年   71篇
  1993年   94篇
  1992年   107篇
  1991年   95篇
  1990年   76篇
  1989年   93篇
  1988年   82篇
  1987年   58篇
  1986年   59篇
  1985年   100篇
  1984年   110篇
  1983年   56篇
  1982年   62篇
  1981年   53篇
  1980年   59篇
  1979年   73篇
  1978年   66篇
  1977年   79篇
  1976年   52篇
  1975年   46篇
  1974年   47篇
  1973年   51篇
排序方式: 共有6314条查询结果,搜索用时 31 毫秒
91.
Photoassisted selective catalytic reduction of NO with ammonia (photo-SCR) at low temperature over irradiated TiO2 in a flow reactor was confirmed to proceed efficiently and the adsorbed ammonia reacted with NO under irradiation of TiO2.  相似文献   
92.
A cationic CpRu(II) complex in combination with quinaldic acid shows high reactivity and chemoselectivity for the catalytic deprotection of hydroxyl groups protected as allyl ethers. The catalyst operates in alcoholic solvents without the need for any additional nucleophiles, satisfying the practical requirements of operational simplicity, safety, and environmental friendliness. The wide applicability of this deprotection strategy to a variety of multifunctional molecules, including peptides and nucleosides, may provide new opportunities in protective group chemistry. [structure: see text]  相似文献   
93.
A molecularly imprinted polymer was prepared using a water-soluble crosslinking agent. An ionic complex was utilized as the assembly for the template molecule and the functional monomer, and water as porogenic solvent during preparation of the imprinted polymer. The results of chromatographic evaluations for the prepared polymer suggested that the polymer had much lower hydrophobicity compared with usual octadecyl group bonded silica or the usual molecular imprinted polymer prepared from ethyleneglycol dimethacrylate, and the selective recognition ability for template molecule in the completely aqueous condition.  相似文献   
94.
Abstract— Structurally controlled aggregation course for five porphyrins (etioporphyrin [EP], 5-mono- and 5,15-di-[ p -tol-yl]etioporphyrin [TP and DTP], 5,10,15,20-tetrakis[ p -tol-y1]porphin [TTP], and 5,10,15,20-tetrakis[3,5-di- tert -bu-tylphenyl]porphin [TBP]) in dipalmitoyl-phosphatidyl-choline liposomes has been monitored by fluorescence and absorption spectroscopy. While TBP shows no tendency to aggregate in liposomes, EP, TP, DTP and TTP form a porphyrin-enriched domain in membrane interior with time. The further aggregation steps within porphyrin clusters resulting in formation of stacked porphyrin aggregates have been observed for EP, TP and DTP.  相似文献   
95.
The host compounds 1,1’-binaphthyl-2,2′-dihydroxy-5,5′-dicarboxylic acid (1) and 1,1′-binaphthyl-2,2′-dihydroxy-6,6′-dicarboxylic acid (2) have been synthesized, and their inclusion properties have been studied. Inclusion complexes formed by 1 and 2 with volatile guests such as acetone and methanol release the guests only at much higher temperatures than their boiling points. The crystal structures of the inclusion complexes have been determined from single crystal X-ray diffraction data and show different host lattices.  相似文献   
96.
The instantaneous elastic moduli for a nylon-6 monofilament were derived on strain recoveries right after creep, stress relaxation, and rapid elongation,E c ,E s andE e , respectively. It was found that during strain recoveryE s (>E e ) andE e increase monotonically with increasing load,m 1, on the sample. The extrapolated value of Es atm 1=0 g is almost equal to Young's modulus, 4.06 GPa. The value ofE c also increased with increasingm 1, and atm 1=600 g (1.93 t cm–2) reached about 14 GPa. The endothermic heat change right after creep, stress relaxation or rapid elongation,Q, was negligibly small. For comparison,E s ,E c andQ were also investigated for silicone rubber. It was found thatE s (53.8 M Pa at the draw ratioD=1.2) decreased abruptly atD=1.3. In the range ofD=1.4–1.9,E s was only 22.6 MPa. In the case of stress relaxation,Q increased with increasingD from 4 J mol–1 (atD=1.2) to 56 J mol–1 (atD=1.9). FurthermoreE c (5.58 MPa atm 1=133.8 g (429.4 kg cm–2)) increased gradually with increasing m1 and attained 16.6 MPa atm 1=548.4 g (1.76 t cm–2). In the case of creep,Q was in the range of 0–11.5 J mol–1 and larger when larger loads,m 2 were removed during the later stages of creep.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe author wishes to thank Mr. Keizi Igarashi and Mr. Tetsuya Yasui for helping in the experiments.  相似文献   
97.
An IgE RIA kit (Sandwich method; Dainabott), is used to obtain the following results. (1) Standard curve: Since the range of reproduction rate show 3.16-7.07% (C.V.), the curve become steep. (2) Incubations under controlled situation: Both of the incubations are controlled at 15-30 degrees C for 2 h. (3) Reproducibility test: Coefficients of variation (C.V.) of intra-assay and inter-assay variation are 2.32-3.94% and 2.92-3.92% respectively. (4) Recovery test: A result of the recovery test range between 100.1-101.7%. (5) Dilution test: Multiple dilution effects are observed. (6) Average counts of the serum IgE for the controlled and diseased groups: The average counts of the serum IgE for the controlled group, atopic diseased group, allergic rhinitis group and allergic bronchial asthma are 144.9 +/- 183.2 IU/ml, 1,099.0 +/- 2,782.4 IU/ml, 1,150.9 +/- 2,063.3 IU/ml and 600.7 +/- 686.4 IU/ml respectively. The value of the diseased groups have tendency to show higher averages than the controlled group. Since the controlled and diseased groups show wide distributions of the serum IgE level, there is no significant difference of two variations. However the diseased groups have tendency to show higher ratio of the serum IgE level in blood than the controlled groups. These basic researches are quite meaningful, because they are able to apply for a supplemental diagnosis of the atopic and parasitic disease.  相似文献   
98.
The Raman and IR spectra of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes have been measured. The normal coordinates have been calculated for these molecules using a consistent set of force constants and the molecular conformations studied by analysing the spectra with reference to the results of the calculations. In the crystalline solid state, 1,5-dichloropentane assumes the trans-trans-trans-gauche form and 1,5-dibromopentane, 1,6-dichloro- and 1,6-dibromohexanes assume the all-trans form. The normal coordinate treatment with the well-established force field was of great help in determining the whole molecular form of the relatively large chain molecules.  相似文献   
99.
The separation and quantitative analysis of streptomyces hyaluronidase ( HAase ) degradation products of hyaluronic acid (HA) by high-performance liquid chromatography are described. The substituted 4,5-unsaturated tetrasaccharide and hexasaccharide which result from the digestion of HA are quickly separated on a silica gel (Zorbax SIL) column. The assay of HA is linear between 5 and 250 micrograms of HA. This procedure is suitable for some weakly acidic glycosaminoglycan contaminants having similar properties to those of HA.  相似文献   
100.
We present a reliable, rapid, and economical multiplex amplified product-length polymorphism (APLP) method for analyzing the haplogroup-diagnostic mitochondrial single-nucleotide polymorphisms (mtSNPs) in East Asian populations. By examining only 36 haplogroup-specific mtSNPs in the coding region by using four 9-multiplex polymerase chain reaction (PCR) and subsequent electrophoresis, we could safely assign 1815 individuals from 8 populations of Japanese, Korean, Chinese, and Germans to 45 relevant haplogroups. This multiplex APLP analysis of coding-region mtSNPs for haplogrouping is especially useful not only for molecular phylogenetic studies but also for large-scale association studies due to its rapid and economical nature. This is the first panel of mtSNPs in the coding region to be used for haplogrouping of East Asian populations.  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