全文获取类型
收费全文 | 2703篇 |
免费 | 60篇 |
国内免费 | 10篇 |
专业分类
化学 | 1970篇 |
晶体学 | 32篇 |
力学 | 33篇 |
数学 | 85篇 |
物理学 | 653篇 |
出版年
2023年 | 17篇 |
2021年 | 18篇 |
2020年 | 28篇 |
2019年 | 22篇 |
2018年 | 23篇 |
2017年 | 32篇 |
2016年 | 34篇 |
2015年 | 39篇 |
2014年 | 42篇 |
2013年 | 127篇 |
2012年 | 116篇 |
2011年 | 135篇 |
2010年 | 90篇 |
2009年 | 91篇 |
2008年 | 151篇 |
2007年 | 142篇 |
2006年 | 132篇 |
2005年 | 120篇 |
2004年 | 126篇 |
2003年 | 117篇 |
2002年 | 104篇 |
2001年 | 68篇 |
2000年 | 59篇 |
1999年 | 30篇 |
1998年 | 34篇 |
1997年 | 27篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 37篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 37篇 |
1990年 | 24篇 |
1989年 | 32篇 |
1988年 | 30篇 |
1987年 | 21篇 |
1986年 | 31篇 |
1985年 | 42篇 |
1984年 | 49篇 |
1983年 | 25篇 |
1982年 | 37篇 |
1981年 | 35篇 |
1980年 | 37篇 |
1979年 | 32篇 |
1978年 | 37篇 |
1977年 | 30篇 |
1976年 | 32篇 |
1975年 | 34篇 |
1974年 | 24篇 |
1973年 | 22篇 |
排序方式: 共有2773条查询结果,搜索用时 15 毫秒
11.
35Cl NQR as well as heat capacity measurements of [(PyO)H][AuCl4] and its deuterated analog [(PyO)D][AuCl4] revealed successive phase transitions at 70.5 and 62.5 K, and at 71 and 63 K, respectively. The NQR frequency varied continuously through the upper transition point while discontinuously through the lower transition point. In the intermediate-temperature phase a remarkable decrease in the signal intensity was observed. These NQR observations as well as the feature of the heat capacity anomaly in which a broad peak is succeeded by a sharp peak with decreasing temperature suggest a possibility of normal-incommensurate-commensurate phase sequence. 相似文献
12.
N Murakami T Tanase S Nagai Y Sato T Ueda J Sakakibara H Ando Y Hotta K Takeya 《Chemical & pharmaceutical bulletin》1991,39(8):1962-1966
The Diels-Alder reactions of a cardiac glycoside, proscillaridin (1), with some dienophiles were investigated. The reaction of 1 with alkenes such as methyl vinyl ketone and methyl acrylate afforded 3-oxo-2-oxabicyclo[2.2.2]oct-7-enes (2-5) and para-substituted benzene derivatives (6 and 7), while 1 reacted with alkynes (3-butyn-2-one, methyl propiolate) to yield para- or meta-substituted benzene derivatives (6-9). The biological activities of the resulting derivatives were evaluated by the use of isolated guinea-pig papillary muscle preparations and Na+,K(+)-adenosine triphosphatase (ATPase) preparation from dog kidney. Among the proscillaridin derivatives, compounds 4 and 7 moderately inhibited Na+,K(+)-ATPase activity. Furthermore, the concentration range of 7 over which its positive inotropic effect on guinea-pig papillary muscle preparations, increased from 5% to 95% of maximum was broader than that of 1, i.e., concentration dependency was maintained over a greater range of concentration. 相似文献
13.
14.
Thermal diffusivity, heat capacity, and density of polyvinyl chloride/polycaprolactone (PVC/PCL) blends were measured by the laser flash method, DSC, and pycnometry, respectively. The thermal conductivity of the PVC/PCL blends was determined from the results. The miscibility of the blend and crystallinity of PCL were determined by DSC. The effect of blend structure on thermal conductivity is discussed. The phase compositions of the PVC/PCL blends are of three types depending on PCL content: i.e., up to 33%, from 33 to 70%, and above 70% PCL by weight. Thermal conductivity, thermal diffusivity, and heat capacity of the PVC/PCL blends are strongly affected by the phase composition of the blend, which changes in a complicated way with PCL content. © 1994 John Wiley & Sons, Inc. 相似文献
15.
The pulse lasers, YAG-, CO2-, and N2-lasers, are examined for use in the cleaning of glass. Cleaning is found to be due to the evaporation and sputtering of stains on the glass by the heat energy of the laser light. Only the N2 laser can be used for the cleaning of the exit surface of the glass (the opposite side to the laser). A laser with a high peak power of about 106J/s and short-pulse duration below 100 ns is found to be necessary in practice. 相似文献
16.
In proportion to the environmental pollution problems caused by organotin compounds, the genotoxicities of tin compounds in the environments have become of interest so as to estimate their safety in recent years. In this work, isolated λ-DNA (double-strand DNA) was incubated with inorganic tin(II) and tin(IV) and five organotin compounds [n-butyltin trichloride, di(n-butyltin) dichloride, methyltin trichloride, dimethyltin dichloride and trimethyltin chloride] in reaction systems both with and without hydrogen peroxide (H2O2) content. The tin compounds tested in this study did not induce DNA breakage in the absence of hydrogen peroxide. Divalent inorganic tin (SnCl2) and tetravalent inorganic tin (SnCl4) caused DNA breakage in the presence of hydrogen peroxide (10 mM), and the DNA damage activity of inorganic tin was much more potent in divalent inorganic tin (SnCl2) than in tetravalent inorganic tin (SnCl4). Divalent inorganic tin (SnCl2) induced DNA breakage in a concentration-dependent fashion at concentrations greater than 0.1 mM of SnCl2 in the presence of hydrogen peroxide (10 mM). DNA breakage was not caused by n-butyltin compounds and methyltin compounds either in the presence or in the absence of hydrogen peroxide. 相似文献
17.
Mitsuru Ueda Tetsuya Abe Mitsuo Oda 《Journal of polymer science. Part A, Polymer chemistry》1992,30(9):1993-1998
Aromatic poly(thioether ketone)s were prepared by the direct polycondensation of aromatic dicarboxylic acids with aryl compounds containing ether or sulfide structures using phosphorus pentoxide/methanesulfonic acid (PPMA) as a condensing agent and solvent. Polycondensation proceeded smoothly and produced aromatic poly(thioether ketone)s with inherent viscosities up to 0.73 dL/g. The synthesis of substituted aryl ketones by the reaction of substituted benzoic acids with aryl compounds in PMMA was studied in detail to demonstrate the feasibility of the reaction for polymer formation. The thermogravimetry of the aromatic poly(thioether ketone)s showed a 10% weight loss in air and nitrogen at around 450 and 460°C, respectively. © 1992 John Wiley & Sons, Inc. 相似文献
18.
Katsuya Sakayori Yuji Shibasaki Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6385-6393
Poly(amic acid)s (PAAs) having the high solution stability and transmittance at 365 nm for photosensitive polyimides have been developed. PAAs with a twisted conformation in the main chains were prepared from 2,2′,6,6′‐biphenyltetracarboxylic dianhydride (2,2′,6,6′‐BPDA) and aromatic diamines. Imidization of PAAs was achieved by chemical treatment using trifluoroacetic anhydride. Among them, the PAA derived from 2,2′,6,6′‐BPDA and 4,4′‐(1,3‐phenylenedioxy)dianiline was converted to the polyimide by thermal treatment. The heating at 300 °C under nitrogen did not complete thermal imidization of PAAs having glass‐transition temperatures (Tg)s higher than 300 °C to the corresponding PIs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6385–6393, 2006 相似文献
19.
20.
Let m be an integer with m3. Let K and K be perfect fields of characteristic p and p such that (p,m)=1 and (p,m)=1, respectively. Moreover let A and A be algebraic function fields over K and K defined by xm+ym=a(0, ak) and xm+ym=a(a0 ak), respectively. Put g=(m–1)(m–2)/2. Denote by M(K,p,a) and M(K,p,a) the Hasse-Witt matrices of A and A with respect to the canonical bases of holomorphic differentials. Then we show that if p+p0(mod.m) then rank M(K,p,a)+rank M(K,p,a)=g and if pp1 (mod.m) then rank M(K,p,a)=rank M(K,p,a). 相似文献