全文获取类型
收费全文 | 15100篇 |
免费 | 2479篇 |
国内免费 | 2783篇 |
专业分类
化学 | 11939篇 |
晶体学 | 348篇 |
力学 | 704篇 |
综合类 | 276篇 |
数学 | 1597篇 |
物理学 | 5498篇 |
出版年
2024年 | 50篇 |
2023年 | 255篇 |
2022年 | 532篇 |
2021年 | 536篇 |
2020年 | 589篇 |
2019年 | 626篇 |
2018年 | 574篇 |
2017年 | 586篇 |
2016年 | 680篇 |
2015年 | 799篇 |
2014年 | 925篇 |
2013年 | 1180篇 |
2012年 | 1315篇 |
2011年 | 1395篇 |
2010年 | 1134篇 |
2009年 | 1076篇 |
2008年 | 1151篇 |
2007年 | 1050篇 |
2006年 | 880篇 |
2005年 | 795篇 |
2004年 | 631篇 |
2003年 | 531篇 |
2002年 | 576篇 |
2001年 | 546篇 |
2000年 | 386篇 |
1999年 | 288篇 |
1998年 | 213篇 |
1997年 | 150篇 |
1996年 | 158篇 |
1995年 | 125篇 |
1994年 | 112篇 |
1993年 | 72篇 |
1992年 | 63篇 |
1991年 | 62篇 |
1990年 | 62篇 |
1989年 | 41篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1986年 | 32篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Lei He Hui‐Min Liu Xiao‐Lan Luo Wen‐Qin Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):o104-o106
The title compound, 2‐{N‐[2‐(2‐hydroxybenzamido)ethylammonioethyl]aminocarbonyl}phenolate, C18H21N3O4, crystallizes in a zwitterionic form as a result of intermolecular proton transfer and possesses a negatively charged phenolate group and a protonated amino group. The 2‐hydroxybenzamide and 2‐(aminocarbonyl)phenolate moieties attached to the two ends of the C—C—N—C—C backbone adopt a cis conformation in relation to this backbone. All N‐ and O‐bound H atoms are involved in hydrogen‐bond formation; the zwitterions are first linked into head‐to‐tail dimers, which are further organized into a two‐dimensional network parallel to the crystallographic bc plane. 相似文献
62.
Anomalous room-temperature specific heats have been seen experimentally by Knapp and coworkers in highT
c
superconductors. The measurements depart from 3N k
B
+
0
T by an amount of order
0
T. We present a theory for this, based on the fact that electronphonon interactions cause both electron band energies
k
n
and phonon frequencies
Q
µ
to be weakly temperature-dependent. First an observation is made which we call Brook's Theorem: the shiftE
k
n
(Q
µ) of the electron energy
k
n
due to adding one phonon in modeQ
µ, is identical to the shift
Q
µ
(k
n) of the phonon energy
Qµ due to adding one electron in the statek
n. Second, we assert that to sufficient accuracy whenT>
D
, entropy of the system of interacting electrons and phonons equals the entropy which would be calculated for non-interacting particles, except that theT-dependent energiesE
kn
(T) and
Q
µ
(T) should be used. A proof to orderu
2 (whereu is phonon displacement amplitude) was given in the thesis of one of us. Third, we use Brook's Theorem to show that the corrections C
el and C
ph to the specific heat due toT-dependence of electron and phonon energies respectively, are identically equal and have order of magnitude
0
T. All these results are valid in adiabatic approximation to orderu
2, and fail at low temperatures where non-adiabatic corrections are large. 相似文献
63.
Studies of the electrochemical behavior of epinephrine at a homocysteine self-assembled electrode 总被引:6,自引:0,他引:6
The self-assembled electrode with the homocysteine monolayer (Hcy/Au) has been characterized by infrared spectroscopy and ac impedance spectroscopy in electrolyte. The Hcy/Au electrode is demonstrated to promote the electrochemical response of epinephrine (E) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (ks) is 2.1×10−2 cm s−1 at the self-assembled electrode. The reduction peak of E can be used to determine the concentration of E in presence of ascorbic acid (AA) owing to the Hcy/Au also promoting the electrochemical oxidation of AA. 相似文献
64.
Bin XIN Dan PU Shao Xiang XIONG* Guang Hui WANG Beijing Mass Spectrometry Center Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2003,14(2)
Recently, capillary electrophoresis/electrospray ionization mass spectrometry (CE/ESI- MS) has been rapidly developed as a powerful analytical tool for charged species ranged from small molecules such as carboxylic acids1, phenolic compounds2, metal species3, tetramines4, herbicides5, drugs and drug metabolites6 to peptides and proteins7, 8. The ESI mode has proven to be sensitive, versatile and relatively easy to use in combination with CE. CE confers rapid analysis and efficient separ… 相似文献
65.
Chen H Li G Zhang FF Sun L Chen HL Zhang SY 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(12):2767-2774
Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed. 相似文献
66.
Schumm BA Koetke DS Adolphsen CE Alexander JP Averill D Barish BC Barklow T Barnett BA Blockus D Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan JM Drell PS Drewer DC Durrett D Elia R Feldman GJ Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Hanson G Harr R Harral B Harris FA Hayes K Hearty C Heusch CA Hildreth MD Himel T Hinshaw DA 《Physical review D: Particles and fields》1992,46(1):453-456
67.
Alam MS Kim IJ Nemati B O'Neill JJ Romero V Severini H Sun CR Wang P Zoeller MM Crawford G Fulton R Gan KK Kagan H Kass R Lee J Malchow R Morrow F Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Skubic P Snow J Bortoletto D Brown DN Dominick J McIlwain RL Miao T Miller DH Modesitt M Schaffner SF Shibata EI Shipsey IP Battle M Ernst J Kroha H Roberts S Sparks K Thorndike EH Wang C Artuso M Goldberg M Haupt T Horwitz N Kennett R Moneti GC Playfer S Rozen Y Rubin P 《Physical review D: Particles and fields》1992,46(11):4822-4827
68.
69.
Hui‐yi Lin Chung‐Hsiung Chen KarinC.S. ChenLiu Shoei‐Sheng Lee 《Helvetica chimica acta》2003,86(1):127-138
Six 14‐membered cyclopeptide alkaloids, i.e., ramosines A–C, mucronine J, and lotusines A and D, were isolated from the roots of Paliurus ramosissimus, and an additional four, hemsines A–D, from the roots of P. hemsleyanus. Among these, ramosines A–C ( 1, 5 , and 6 , resp.) and hemsines A and B ( 7 and 8 , resp.) are new bases of the amphibine‐B type, and hemsines C and D ( 9 and 10 , resp.) are new integerrine‐type alkaloids. Additionally, ramosine C ( 6 ) represents the first 14‐membered cyclopeptide alkaloid possessing a substitution (? OH) at C(13′). Their structural elucidations were based on spectral analysis and molecular‐modeling studies. Pronounced solvent effects in the 1H‐ and 13C‐NMR spectra of these two types of alkaloids were observed. 相似文献
70.
Addition of human plasma low-density lipoproteins (LDL) to intact human erythrocytes induces the erythrocytes to undergo morphologic transition from biconcave disks to echinocytes and spherocytes. The transformation is time-dependent. Two hours are required before echinocytes are detected by scanning electron microscopy. After two hours, LDL also decrease the phosphate content of spectrin by 40% relative to the control, suggesting that these lipoproteins modulate cell shape by influencing phosphorylation-dephosphorylation of a membrane-associated cytoskeletal protein. LDL do not induce depletion of intracellular adenosine triphosphate (ATP), nor do they inhibit cyclic adenosine monophosphate-independent protein kinases which phosphorylate spectrin. LDL stimulate membrane-bound phosphatases by a factor of two, thereby reducing the amount of phosphate covalently bound to membrane proteins. The observed effects are specific for LDL. High-density lipoproteins (HDL) do not stimulate dephosphorylation of spectrin or alter erythrocyte morphology. However, HDL protect the erythrocytes against LDL-induced alterations. These data suggest that the circulating lipoproteins have a role in maintaining erythrocyte morphology by regulating the extent of phosphorylation of spectrin. 相似文献