全文获取类型
收费全文 | 28821篇 |
免费 | 4194篇 |
国内免费 | 2412篇 |
专业分类
化学 | 20212篇 |
晶体学 | 552篇 |
力学 | 1064篇 |
综合类 | 273篇 |
数学 | 957篇 |
物理学 | 12369篇 |
出版年
2024年 | 52篇 |
2023年 | 249篇 |
2022年 | 615篇 |
2021年 | 782篇 |
2020年 | 901篇 |
2019年 | 861篇 |
2018年 | 789篇 |
2017年 | 1086篇 |
2016年 | 1327篇 |
2015年 | 1273篇 |
2014年 | 1463篇 |
2013年 | 2732篇 |
2012年 | 1813篇 |
2011年 | 1722篇 |
2010年 | 1478篇 |
2009年 | 1638篇 |
2008年 | 1654篇 |
2007年 | 1658篇 |
2006年 | 1554篇 |
2005年 | 1431篇 |
2004年 | 1384篇 |
2003年 | 1113篇 |
2002年 | 1151篇 |
2001年 | 789篇 |
2000年 | 801篇 |
1999年 | 692篇 |
1998年 | 585篇 |
1997年 | 486篇 |
1996年 | 436篇 |
1995年 | 471篇 |
1994年 | 340篇 |
1993年 | 308篇 |
1992年 | 286篇 |
1991年 | 197篇 |
1990年 | 198篇 |
1989年 | 150篇 |
1988年 | 167篇 |
1987年 | 141篇 |
1986年 | 124篇 |
1985年 | 108篇 |
1984年 | 95篇 |
1983年 | 49篇 |
1982年 | 83篇 |
1981年 | 43篇 |
1980年 | 35篇 |
1979年 | 47篇 |
1978年 | 15篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Christian Borgs Roman Kotecký Salvador Miracle-Solé 《Journal of statistical physics》1991,62(3-4):529-551
Recently, Borgs and Kotecký developed a rigorous theory of finite-size effects near first-order phase transitions. Here we apply this theory to the ferromagneticq-state Potts model, which (forq large andd2) undergoes a first-order phase transition as the inverse temperature is varied. We prove a formula for the internal energy in a periodic cube of side lengthL which describes the rounding of the infinite-volume jumpE in terms of a hyperbolic tangent, and show that the position of the maximum of the specific heat is shifted by
m
(L)=(Inq/E)L
–d
+O(L
–2d
) with respect to the infinite-volume transition point
t
. We also propose an alternative definition of the finite-volume transition temperature
t
(L) which might be useful for numerical calculations because it differs only by exponentially small corrections from
t
. 相似文献
972.
973.
A rapid, sensitive, and convenient spectrophotometric assay was developed for the measurement of amino groups on solid supports.
This method is based on the reaction of amino groups of solids with an excess ofo-phthaldialdehyde (OPA) and subsequent quantitative determination of unreacted OPA by reaction with glycine. Four solids possessing
variable quantities of amino groups were examined. Results indicate that about 70% of the total surface amino concentration
(determined by the microKjeldahl method) are available for ligand attachment. Unlike the spectrophotometric 2,4,6-trinitrobenzenesulfonic
acid method, the OPA spectrophotometric assay is more rapid, sensitive, and convenient, and unlike the spectrofluorimetric
OPA, it does not require sophisticated instrumentation. 相似文献
974.
C. Yeung T. Rogers A. Hernandez-Machado David Jasnow 《Journal of statistical physics》1992,66(3-4):1071-1088
We study phase separation dynamics in a driven diffusive system. Our simulations are based on the Cahn-Hilliard equation with an additional flux term due to an external field. We study the dynamical scaling parallel and perpendicular to the field. A crossover is observed from isotropic domains at early times to extremely anisotropic domains at later times. We find that the inverse interfacial density (an isotropic measure of the domain size) increases ast
, with =1/3, from early times independent of the field strength, even though we do not observe dynamical scaling during these times. Our results indicate that a growth exponent =1/3 may be more universal than previously expected. We analyze the dynamics in terms of surface driven instabilities and one-dimensional solitary waves. 相似文献
975.
We present a study of finite-size effects in a model exhibiting a first-order temperature-driven symmetry-breaking structural phase transition in theL
× cylindrical geometry in theL
limit. Exact studies demonstrate the applicability of our scaling ansatz even in the one-dimensional limit, making this model ideal for studying finite-size effects. The scaling ansatz, similar to the previously developed ansatz for field-driven transitions, demonstrates that latent heat is crucial in driving these transitions. This ansatz is supported by a 2×2 phenomenological transfer matrix based upon the symmetries of the system; this produces an analytic free energy which has the scaling form. Order parameter probability distributions show that the high- and low-temperature phases coexist only in a small finite-size-affected regime near the bulk transition temperature; this regime vanishes exponentially fast asL
diverges. 相似文献
976.
Craig C. Martens 《Journal of statistical physics》1992,68(1-2):207-237
We describe our work on qualitative methods for visualizing the quantum eigenstates of systems with nonlinear classical dynamics. For two-degree-of-freedom systems, our approach is based on the use of generalized coherent states, and allows systems with nonoscillator kinematics to be investigated. The general approach is illustrated with two examples involving vibration-rotation interaction in polyatomic molecules. We apply the coherent states of the Lie groupH
4SU(2) to define quantum surfaces of section for a model involving centrifugal coupling of a harmonic bend with molecular rotation, andSU(2)SU(2) coherent states to study two harmonic normal modes coupled to overall molecular rotation through coriolis interaction. In both systems, quantum states are visualized on the rotational surface of section and compared with the corresponding classical phase space structure. Striking classical-quantum correspondence is observed. We then describe recent results on the quantum states of (N 3)-dimensional systems of coupled nonlinear oscillators, which reveal a quantum delocalization that is reminiscent of classical Arnold diffusion. 相似文献
977.
Ptilomycalin A and crambescidins, novel marine guanidine alkaloids, have a unique pentacyclic guanidine structure, and exhibit a considerable array of biological activities. The first method developed for the synthesis of the pentacyclic guanidine core structure involved successive 1,3-dipolar cycloaddition reactions and resulted in the first total synthesis of crambescidin 359. The synthesis of other pentacyclic guanidine derivatives has been based on this methodology and applied as tools for studying biological activities, and as chemical reaction catalysts. 相似文献
978.
液晶性芳香酰胺化合物的合成 总被引:7,自引:0,他引:7
合成了一系列炖粹以酰胺基为中心桥键的刚性芳香酰胺小分子化合物,并对其作了表征,发现其中有些化合物具有液晶性。酰胺键之间能形成很强的分子间氢键,使芳香酰胺小分子化合物的熔点很高,难于形成液成液晶态。研究发现,如果在这类化合物的中心苯环上引入合适的取代基以减弱分子间氢键,同时引入合适的末端基时,则可使芳香酰胺化合物生成液晶相的能力增强。 相似文献
979.
《Arabian Journal of Chemistry》2022,15(12):104368
Protein hydrolysates have the potential to be natural and safer sources of bioactive peptides. In this study, two proteases were used to hydrolyze Chinese sturgeon (Acipenser sinensis) protein, and the hydrolysates were then purified to yield antioxidant peptides. The degree of hydrolysis of 23.56 % and 18.14 % was obtained using papain and alcalase 2.4L, respectivly, and hydrolysates had 96.80 % and 87.24 % total amino acid content, respectivly. The papain hydrolysate (PH) and alcalase 2.4L hydrolysate (AH) showed good antioxidant activity against DPPH? (IC50 of 3.64 and 3.15 mg/mL) and ABTS?+ (IC50 of 1.92 and 1.58 mg/mL), respectively. The low-molecular-weight (<1000 Da) fraction of both hydrolysates demonstrated the highest antiradical activity (IC50 of 2.59 and 2.31 mg/mL, DPPH) and (IC50 of 1.54 and 1.36 mg/mL, ABTS), respectively. Nine peptides were separated from both hydrolysates using reverse phase high performance liquid chromatography (RP-HPLC). The IC50 for ABTS?+ scavenging activity of peptide P5 with valine, glycine and asparagine (MW of 282.13 Da) from PH, and peptide P3 with histidine, glycine and alanine (MW of 302.74 Da) from AH was 0.89 and 0.72 mg/mL, respectively. The fractions and purified peptides obtained from Chinese sturgeon hydrolysates could be utilized as natural antioxidant substitutes in pharmaceuticals and food products. 相似文献
980.
建立了分散固相萃取净化-超高效液相色谱-串联质谱法快速测定鱼和虾中3类(磺胺类、喹诺酮类、氯霉素类)18种抗生素及2种三苯甲烷类(孔雀石绿、隐色孔雀石绿)兽药残留。样品经磷酸氢二钾溶液水解分散,乙腈提取,提取液经氯化钠脱水、盐析后取乙腈层,经旋转蒸发仪浓缩至近干,残留物用甲醇定容至1.0 mL,C18和PSA(N-丙基乙二胺)填料分散固相萃取净化,过滤膜后经ZORBAX C18色谱柱(50 mm×2.1 mm,1.8 μm)分离,正、负离子多反应监测模式采集数据,同位素内标法定量。实验结果表明,20种兽药在0.2~300 μg/L范围内具有良好的线性关系,检出限为0.1~0.6 μg/kg,定量限为0.3~1.8 μg/kg,相关系数均大于0.99。在1、5和20倍定量限加标浓度水平下,平均回收率为72.5%~118%,相对标准偏差(RSD)为1.9%~9.8%。该方法具有前处理简单、检测效率高、成本低等优点,适用于鱼和虾中多类兽药残留的同时测定。 相似文献