全文获取类型
收费全文 | 83712篇 |
免费 | 2172篇 |
国内免费 | 358篇 |
专业分类
化学 | 46339篇 |
晶体学 | 1237篇 |
力学 | 2996篇 |
综合类 | 2篇 |
数学 | 9660篇 |
物理学 | 26008篇 |
出版年
2023年 | 954篇 |
2022年 | 838篇 |
2021年 | 1175篇 |
2020年 | 1643篇 |
2019年 | 1270篇 |
2018年 | 2302篇 |
2017年 | 2639篇 |
2016年 | 2402篇 |
2015年 | 1578篇 |
2014年 | 2850篇 |
2013年 | 6811篇 |
2012年 | 4466篇 |
2011年 | 5504篇 |
2010年 | 3933篇 |
2009年 | 3945篇 |
2008年 | 3970篇 |
2007年 | 4090篇 |
2006年 | 3463篇 |
2005年 | 2831篇 |
2004年 | 2190篇 |
2003年 | 2058篇 |
2002年 | 1680篇 |
2001年 | 1604篇 |
2000年 | 1173篇 |
1999年 | 1404篇 |
1998年 | 982篇 |
1997年 | 804篇 |
1996年 | 662篇 |
1995年 | 683篇 |
1994年 | 681篇 |
1993年 | 635篇 |
1992年 | 588篇 |
1991年 | 600篇 |
1990年 | 601篇 |
1989年 | 741篇 |
1988年 | 1118篇 |
1987年 | 570篇 |
1986年 | 515篇 |
1985年 | 850篇 |
1984年 | 946篇 |
1983年 | 495篇 |
1982年 | 766篇 |
1981年 | 717篇 |
1980年 | 759篇 |
1979年 | 652篇 |
1978年 | 608篇 |
1977年 | 604篇 |
1976年 | 567篇 |
1975年 | 386篇 |
1973年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
V. Natarajan T. K. Seshagiri A. G. Page 《Journal of Radioanalytical and Nuclear Chemistry》1994,187(2):123-129
Electron paramagnetic resonance (EPR) studies of -irradiated uranium doped BaCO3 have shown the formation of CO3
–, CO2
–, O3
– and O2
– ions. Thermally stimulated luminescence (TSL) glow curves of the -irradiated samples in the 300–600 K range have exhibited an intense peak around 360 K and a weak one around 440 K. The trap parameters for these peaks have been determined from TSL data. Spectral studies of the glow have revealed emission around 566, 583 and 590 nm characteristic of the uranate ion. From studies on the thermal stabilities of the radical ions, it has been inferred that the glow peak around 360 K is associated with the thermal destruction of O2
– ion and the peak around 440 K is associated with the thermal destruction of CO3
– ion. 相似文献
992.
An attempt js made to study the behaviour of recoil128I atoms in neutron irradiated I2O5 at ambient temperature. The initial retention is found to be 44±2%. However, a substantial increase /57±2%/ in the value is observed upon heating the sample at 473 K for 1 h prior to irradiation. A kinetic study of post-recoil thermal annealing of neutron irradiated material is also presented. Effect of pre-heat treatment results in a decrease of rate constants and saturation retention values at respective temperatures while the Eact for the overall process remains almost unaltered. 相似文献
993.
Synthesis of cis-hydrindane analogues (2,3) of Cecropia juvenile hormone-I from common intermediate cis-hydrindane-2, 5-dione is presented. The analogues are only moderately active against Dysdercus cingulatus. 相似文献
994.
Anil P. Phadnis Bharati Sinha Bhagbat Nanda Sarita A. Patwardhan J. Venkatesh Rao Ravindra N. Sharma 《Monatshefte für Chemie / Chemical Monthly》1989,120(6-7):581-586
Summary A series of 8-proparglyoxy-3,7-dimethyl-2,6-octadienyl and 8-propargyloxy-3,7-dimethyl-6-octenyl ethers were prepared from 8-hydroxygeranyl and 8-hydroxycitronellyl ethers, respectively. Almost all compounds showed high toxicity toCulex quinquefaciatus larvae at 1 mgl–1 dose level.
Gegen Mücken aktive Produkte, 4. Mitt.: Synthese und biologische Aktivität von 8-Propargyloxy-3,7-dimethyl-2,6-octadienyl/6-octenyl-ethern
Zusammenfassung Eine Reihe von 8-Propargyloxy-3,7-dimethyl-2,6-octadienyl- und 8-propargyloxy-3,7-dimethyl-6-octenyl-ethern wurden aus 8-Hydroxygeranyl- bzw. 8-Hydroxycitronellyl-ethern hergestellt. Fast alle Verbindungen zeigten hoch Toxizität gegenüber Larven vonCulex quinquefaciatus in einer Dosierung von 1 mgl–1.相似文献
995.
P. N. Chaturvedi M. J. Patel K. C. Patel R. D. Patel 《Colloid and polymer science》1987,265(7):592-596
The film formation method has been successfully used to grow single crystals and other complex morphological features of low melting form (LMF) and high melting form (HMF) of trans-1,4-polyisoprene (TPIP). Below 40 °C dilute amyl acetate solution gave hexagonal shaped LMF crystals. Thick and elongated hexagonal shaped morphology was shown by HMF crystals at temperatures above 40 °C. Straight faces and sharp corners of the single crystals, and also of complex crystals, acquired round shapes when highly polydispersed TPIP was used for crystallization. 相似文献
996.
Sukhendu Mandal 《Journal of solid state chemistry》2004,177(6):2198-2204
A solvothermal reaction of ZnO, HCl, H3PO4, and N,N′(3-bisaminopropyl)-1,2-ethylenediamine (BAPEN) in diethyleneglycol at 160°C yields a new zinc chlorophosphate, [C8N4H26][Zn3Cl(HPO4)3(PO4)], I. The structure comprises ZnO4, ZnO3Cl, HPO4 and PO4 tetrahedral units connected through their vertices giving rise to a layered structure with 10-membered apertures. The position of the Zn and P atoms gives rise to double-four ring like building unit with one Zn missing. The fully protonated amine molecules occupy the inter-lamellar region and interacts with the framework through N-H?O hydrogen bonds. Crystal data: M=792.85, orthorhombic, space group=Pca21 (no. 29), a=9.8410(2), b=15.0912(2), c=16.1220(4) Å, V=2394.32(8) Å3, Z=4, ρcalc=2.199 g cm−3, μ(MoKα)=3.443 mm−1, R1=0.0520, wR2=0.1256 and S=1.054. 相似文献
997.
The excited-state photophysical properties of curcumin in the presence of bovine serum albumin (BSA) have been studied. The absorption and fluorescence changes in curcumin on binding to BSA have been followed at varying concentrations of either curcumin or BSA to determine the binding constant, which has been found to be approximately 10(4) to 10(5) M(-1). Stopped-flow kinetics studies suggested at least two distinct kinetic steps for the binding of curcumin to BSA. The photophysical properties of the singlet-excited state of the curcumin-BSA complex have also been studied. Whereas the absorption spectrum of curcumin is redshifted, the fluorescence spectrum of curcumin was blueshifted in the presence of BSA. The fluorescence quantum yield of curcumin on complexing with BSA was approximately 0.05. Steady-state fluorescence anisotropy studies showed a significant increase in the anisotropy value of 0.37 in BSA-bound curcumin. The fluorescence decay of the curcumin-BSA complex followed a biexponential decay with fluorescence lifetimes of 413 ps (33%) and 120 ps (67%). On the basis of these complementary results, it has been concluded that curcumin shows very high binding to BSA, probably at the hydrophobic cavities inside the protein. 相似文献
998.
Ammonium acetate was found to catalyze efficiently the selective deprotection of aromatic acetates in the presence of various sensitive functionalities in aqueous methanol under neutral conditions at room temperature to yield the corresponding phenols in excellent yields. The method has been utilized for deprotection of acetates of several naturally occurring bioactive phenolic compounds and for preparation of venkatasin, a natural coumarino-lignan, from the anticancer compound cleomiscosin A. 相似文献
999.
C. K. Radhakrishnan A. Sujith G. Unnikrishnan 《Journal of Thermal Analysis and Calorimetry》2007,90(1):191-199
The thermal behaviour of styrene butadiene rubber (SBR)/poly (ethylene-co-vinyl acetate) (EVA) blends was studied by using
thermogravimetry (TG) and differential scanning calorimetry (DSC). The effects of blend ratio, cross-linking systems and compatibilization
on the thermal stability and phase transition of the blends were analyzed. It was found that the mass loss of the blends at
any temperature was lower than that of the components, highlighting the advantage of blending SBR and EVA. The addition of
compatibilizer was also found to improve the thermal stability. DSC studies indicated the thermodynamic immiscibility of SBR/EVA
system even in the presence of the compatibilizer. This is evident from the presence of two different glass transition temperatures,
corresponding to SBR and EVA phases in both compatibilized and uncompatibilized blends. 相似文献
1000.
U. Pandey S. Banerjee A. Mukherjee H. D. Sarma M. Venkatesh 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):719-723
Several human tumors such as neuroendocrine tumors, medullary thyroid carcinoma, etc., express somatostatin receptors which
specifically bind somatostatin and its analogues such as lanreotide, octreotide, etc. In order to prepare a therapeutic agent
for targeting such tumors, attempts were made to prepare 90Y-DOTA-Lanreotide. Lanreotide could be successfully conjugated with the macrocyclic chelating agent DOTA (1,4,7,10-tetraaza
cyclododecane tetracetic acid) which forms stable complexes with 90Y. 90Y-DOTA-Lanreotide could be prepared in >98% radiochemical purity and remained stable for 72 hours at room temperature. The
tracer showed specific binding to A431 cells. Biodistribution studies in C57BL6 mice bearing melanoma showed ∼1.3% uptake
pergram of tumor at 24-hour p.i. 相似文献