全文获取类型
收费全文 | 11681篇 |
免费 | 316篇 |
国内免费 | 46篇 |
专业分类
化学 | 5948篇 |
晶体学 | 172篇 |
力学 | 279篇 |
数学 | 752篇 |
物理学 | 3179篇 |
无线电 | 1713篇 |
出版年
2023年 | 139篇 |
2022年 | 290篇 |
2021年 | 269篇 |
2020年 | 297篇 |
2019年 | 324篇 |
2018年 | 302篇 |
2017年 | 302篇 |
2016年 | 409篇 |
2015年 | 241篇 |
2014年 | 469篇 |
2013年 | 891篇 |
2012年 | 625篇 |
2011年 | 710篇 |
2010年 | 449篇 |
2009年 | 450篇 |
2008年 | 520篇 |
2007年 | 502篇 |
2006年 | 388篇 |
2005年 | 331篇 |
2004年 | 262篇 |
2003年 | 208篇 |
2002年 | 210篇 |
2001年 | 139篇 |
2000年 | 147篇 |
1999年 | 105篇 |
1998年 | 77篇 |
1997年 | 83篇 |
1996年 | 124篇 |
1995年 | 132篇 |
1994年 | 132篇 |
1993年 | 121篇 |
1992年 | 143篇 |
1991年 | 113篇 |
1990年 | 97篇 |
1989年 | 106篇 |
1988年 | 104篇 |
1987年 | 101篇 |
1986年 | 80篇 |
1985年 | 124篇 |
1984年 | 136篇 |
1983年 | 103篇 |
1982年 | 108篇 |
1981年 | 107篇 |
1980年 | 119篇 |
1979年 | 96篇 |
1978年 | 104篇 |
1977年 | 89篇 |
1976年 | 64篇 |
1975年 | 66篇 |
1974年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Signs of the dipole moment derivatives, ?px/?S4 and ?px/?S5 where px is the dipole moment vector along an axis perpendicular to the CO bond in the plane of the molecule and Sj are the symmetry coordinates for the B1 vibrations of Br2CO have been re-evaluated from the reported ?p/?Qi values (p being the dipole moment of the molecule and Qi the normal coordinates) and the L matrix elements. The new set of dipole moment derivatives fits well with similar parameters for Cl2CO and F2CO. 相似文献
82.
Sukumar Aditya Syamal Bandopadhyay Rebati C. Das Bata K. Nanda 《Thermochimica Acta》1981,46(3):337-340
From rehydration experiments the hydrates Ba(OH)2 · 8 H2O, Ba(OH)2 · 3 H2O β-Ba(OH)2, · 1 H2O, and γ-Ba(OH)2 · 1 H2O have been found in the system Ba(OH)2-H2O. Thermoanalytical measurements (DTA, TG, DTG, high temperature X-ray diffraction, high temperature Raman scattering) on these hydrates are reported. Thermal decomposition of Ba(OH)2 · 8 H2O and Ba(OH)2 · 3 H2O always results in the formation of β-Ba(OH)2 · 1 H2O, the stable form of the monohydrates at ambient temperature. Dehydration of β- and γ-Ba(OH)2 · 1 H2O, both of which form anhydrous β-Ba(OH)2 as the first product of decomposition, starts at 105 and 115°C, respectively. Single crystals of Ba(OH)2 · 3 H2O and γ-Ba(OH)2 · 1 H2O were prepared from Ba(OH)2 · 8 H2O meltings and from ethanolic solutions of Ba(OH)2 , respectively. The crystal data are: Ba(OH)2 · 3 H2O (orthorhombic, Pnma): a = 764.0(2), b = 1140,3(5), c = 596.5(1) pm, Z = 4; γ-Ba(OH)2 · 1 H2O (monoclinic, P21/m or P21): a = 704.9(2), b = 418.4(1), c = 633.3(1) pm, β = 111.45(2)°, Z = 2. 相似文献
83.
The specifically designed reagent, 4-tButyl iodoxybenzene (1)-soluble in hot, benzene, chlorobenzene and nitrobenzene- cleaves a range of π bonds to carbonyl compounds in 50–75% isolated yields. In every case, the reagent 1 is transformed to 4-tbutyl iodobenzene (2) in 90–97% yields, which can be recycled. 相似文献
84.
Human antibody 2G12 broadly neutralizes human immunodeficiency virus type 1 (HIV-1) isolates and shows protective activity against viral challenge in animal models. Previous mutational analysis suggested that 2G12 recognized a novel cluster of high-mannose type oligosaccharides on HIV-1 gp120. To explore the carbohydrate antigen for HIV-1 vaccine design, we have studied the binding of 2G12 to an array of HIV-1 high-mannose type oligosaccharides by competitive ELISAs and found that Man9GlcNAc is 210- and 74-fold more effective than Man5GlcNAc and Man6GlcNAc in binding to 2G12. The results establish that the larger high-mannose oligosaccharide on HIV-1 is the favorable subunit for 2G12 recognition. To mimic the putative epitope of 2G12, we have created scaffold-based multivalent Man9 clusters and found that the galactose-scaffolded bi-, tri-, and tetra-valent Man9 clusters are 7-, 22-, and 73-fold more effective in binding to 2G12 than the monomeric Man9GlcNAc2Asn. The experimental data shed light on further structural optimization of epitope mimics for developing a carbohydrate-based HIV-1 vaccine. 相似文献
85.
Sham M. Sondhi Shefali Rajvanshi Nirupma Singh Shubhi Jain Anand M. Lahoti 《Central European Journal of Chemistry》2004,2(1):141-187
Non steroidal anti-inflammatory drugs are the most widely used medicines for relief of pain. These drugs have some side effects,
particularly toxicity in the gastrointestinal tract and kidneys. Various approaches have been used for obtaining safer anti-inflammatory
drugs. In this review we have summarized the recent developments in the following areas; (i) mode of action of NSAIDs (ii)
Role of COX-1 & COX-2 in inflammation, (iii) Different approaches used to improve gastric tolerance i.e. chemical manipulation,
formulation & co-administration, development of non specific (COX-1 & COX-2 inhibitors) and specific (COX-2 inhibitors) inflammation
inhibitors, and development of inflammation inhibitors having a mode of action other than COX-1 & COX-2 inhibition. We have
also focused on the safety of COX-2 inhibitors and the synthesis of heterocyclic compounds and their role as inflammation
inhibitors. 相似文献
86.
Devendrapratap U Singh 《Tetrahedron letters》2004,45(24):4805-4807
Fe-exchanged montmorillonite K10 catalyzes a highly efficient reaction between sterically and electronically diverse sulfonamides and carboxylic acid anhydrides to furnish N-acylsulfonamides in excellent yield and high selectivity. The catalyst can also be reused several times. 相似文献
87.
Satwinder Singh 《Tetrahedron letters》2004,45(33):6349-6352
Epoxidation of the allylic alcohols 10 and 11 using the VO(acac)2/t-BuOOH system followed by an intramolecular 5-exo cyclization of the resulting δ-epoxycarbamates 12, 13, 18, and 19 has been shown to provide a general and efficient solution for the asymmetric synthesis of polyhydroxy pyrrolidines. The requisite vicinal amino alcohol functionality was enantio-/regio-selectively installed by the Os-catalyzed asymmetric aminohydroxylation reaction of the designed achiral olefin 6. 相似文献
88.
Chloramine-B has been used as an oxidizing agent in hydrochloric acid medium for the indirect volumetric estimations of hydrogen peroxide, lead dioxide, manganese dioxide, selenium dioxide, sodium formate, sodium sulphide, sodium metavanadate, potassium iodate and copper sulphate using iodine monochloride as a catalyst and pre-oxidiser. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes light pale yellow at the end-point because of the formation of iodine monochloride. 相似文献
89.
Xiaona Wen Yu-Chuan Ou Galina Bogatcheva Giju Thomas Anita Mahadevan-Jansen Bhuminder Singh Eugene C. Lin Rizia Bardhan 《Chemical science》2020,11(36):9863
Rapid and accurate response to targeted therapies is critical to differentiate tumors that are resistant to treatment early in the regimen. In this work, we demonstrate a rapid, noninvasive, and label-free approach to evaluate treatment response to molecular inhibitors in breast cancer (BC) cells with Raman spectroscopy (RS). Metabolic reprogramming in BC was probed with RS and multivariate analysis was applied to classify the cells into responsive or nonresponsive groups as a function of drug dosage, drug type, and cell type. Metabolites identified with RS were then validated with mass spectrometry (MS). We treated triple-negative BC cells with Trametinib, an inhibitor of the extracellular-signal-regulated kinase (ERK) pathway. Changes measured with both RS and MS corresponding to membrane phospholipids, amino acids, lipids and fatty acids indicated that these BC cells were responsive to treatment. Comparatively, minimal metabolic changes were observed post-treatment with Alpelisib, an inhibitor of the mammalian target of rapamycin (mTOR) pathway, indicating treatment resistance. These findings were corroborated with cell viability assay and immunoblotting. We also showed estrogen receptor-positive MCF-7 cells were nonresponsive to Trametinib with minimal metabolic and viability changes. Our findings support that oncometabolites identified with RS will ultimately enable rapid drug screening in patients ensuring patients receive the most effective treatment at the earliest time point.Rapid and accurate response to targeted therapies is critical to differentiate tumors that are resistant to treatment early in the regimen. 相似文献
90.
Krishna Raman Surendra S. Parmar Shiva P. Singh 《Journal of heterocyclic chemistry》1980,17(5):1137-1139
A series of 1-(5-phenyl-2H-tetrazol-2-ylacetyl)-4-substituted thiosemicarbazids were prepared as possible antiinflammatory agents. Their antiproteolytic activity was reported. 相似文献