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311.
Minakawa N Kojima N Hikishima S Sasaki T Kiyosue A Atsumi N Ueno Y Matsuda A 《Journal of the American Chemical Society》2003,125(33):9970-9982
The synthesis and thermal stability of oligodeoxynucleotides (ODNs) containing imidazo[5',4':4,5]pyrido[2,3-d]pyrimidine nucleosides 1-4 (N(N), O(O), N(O), and O(N), respectively) with the aim of developing two sets of new base pairing motifs consisting of four hydrogen bonds (H-bonds) is described. The proposed four tricyclic nucleosides 1-4 were synthesized through the Stille coupling reaction of a 5-iodoimidazole nucleoside with an appropriate 5-stannylpyrimidine derivative, followed by an intramolecular cyclization. These nucleosides were incorporated into ODNs to investigate the H-bonding ability. When one molecule of the tricyclic nucleosides was incorporated into the center of each ODN (ODN I and II, each 17mer), no apparent specificity of base pairing was observed, and all duplexes were less stable than the duplexes containing natural G:C and A:T pairs. On the other hand, when three molecules of the tricyclic nucleosides were consecutively incorporated into the center of each ODN (ODN III and IV, each 17mer), thermal and thermodynamic stabilization of the duplexes due to the specific base pairings was observed. The melting temperature (T(m)) of the duplex containing the N(O):O(N) pairs showed the highest T(m) of 84.0 degrees C, which was 18.2 and 23.5 degrees C higher than that of the duplexes containing G:C and A:T pairs, respectively. This result implies that N(O)and O(N) form base pairs with four H-bonds when they are incorporated into ODNs. The duplex containing N(O):O(N) pairs was markedly stabilized by the assistance of the stacking ability of the imidazopyridopyrimidine bases. Thus, we developed a thermally stable new base pairing motif, which should be useful for the stabilization and regulation of a variety of DNA structures. 相似文献
312.
Benten H Ohkita H Ito S Yamamoto M Sakumoto N Hori K Tohda Y Tani K Nakamura Y Nishimura J 《The journal of physical chemistry. B》2005,109(42):19681-19687
The photophysical properties of a series of triply bridged [3.3.n](3,6,9)carbazolophanes ([3.3.n]Cz, n = 3, 4, 5, 6) were studied as a model compound for a fully overlapped carbazole excimer. In these [3.3.n]Cz molecules, a plane angle of the two carbazole moieties changed systematically from nearly parallel to oblique, with increases in the length of the methylene chain n bridging at the 9-position of each carbazole ring. Absorption bands of [3.3.n]Cz showed the blue-shift and the splitting for (1)L(a) <-- (1)A and (1)L(b) <-- (1)A transition bands of the reference carbazole monomer, respectively. These spectral changes in [3.3.n]Cz were explained by Kasha's molecular exciton theory with the distance r and dihedral angle theta between the carbazole moieties in the ground state. In both liquid and glass matrixes, [3.3.n]Cz showed intramolecular excimer emission. The emission peak wavelength changed from 409 nm (n = 6) to 480 nm (n = 3) depending on r in the ground state. The dependence of the peak wavelength on r clearly showed that relative configurations of carbazole moieties in the ground state were preserved even in the excimer states. The smaller radiative rate of the excimer emission than the reference monomer was explained by the dimer symmetry of [3.3.n]Cz. 相似文献
313.
T Sawayama M Tsukamoto T Sasagawa K Nishimura R Yamamoto T Deguchi K Takeyama K Hosoki 《Chemical & pharmaceutical bulletin》1989,37(9):2417-2422
A new series of gamma-D-Glu-containing N-benzyloxycarbonyl (Z) tripeptide inhibitors of angiotensin-converting enzyme (ACE) was synthesized. The effect of varying the antepenultimate amino acid residue in this series on the biological activity was studied. Introduction of Lys and Orn residues at the P1 position provided the most potent inhibitors, 25a and 25b (IC50: 3.5 and 4.9 x 10(-9) M, respectively), which exhibited an oral antihypertensive activity. This result suggests that basic amino acid residues at the P1 position play an important role in binding with the S1 subsite of ACE in this series. Oral antihypertensive activity of selected compounds was evaluated. 相似文献
314.
Takayuki Otsu Shuzo Aoki Masato Nishimura Masami Yamaguchi Yoshihiro Kusuki 《Journal of polymer science. Part A, Polymer chemistry》1969,7(12):3269-3277
The polymerizations of methyl methacrylate, styrene, and isobutyl vinyl ether with the binary systems of reduced nickel and chlorosilanes [(CH3)nSiCl4?n, n = 0–3] have been investigated. It was found that these systems could act as both radical and cationic initiators, depending on the nature of vinyl monomers used. The kinetic investigations indicated that methyl methacrylate polymerized via a radical mechanism, and the initiating activity of chlorosilanes decreased in the following order: SiCl4 > CH3SiCl3 > (CH3)2SiCl2 > (CH3)3SiCl ? 0. Cationic initiations were observed in the polymerizations of styrene and isobutyl vinyl ether. In the latter case, the activity of chlorosilanes was in the following order: (CH3)3SiCl > (CH3)2SiCl2 > CH3SiCl3 ? SiCl4. From the results obtained, a possible mechanism of selective initiation with these systems is proposed and discussed. 相似文献
315.
Hirobumi Takahashi Takehiro Fukami Hisaki Kojima Takeru Yamakawa Hiroyuki Takahashi Toshihiro Sakamoto Teruyuki Nishimura Masayuki Nakamura Takashi Yosizumi Kenji Niiyama Norikazu Ohtake Takashi Hayama 《Tetrahedron》2005,61(14):3473-3481
A robust synthetic method for 2-alkylamino-6-carboxy-5,7-diarylcyclopenteno[1,2-b]pyridines via acylamination at the alpha position of the functionalized pyridine system has been developed. The key step in this method was achieved by treatment of the corresponding pyridine N-oxides with 2.5 equiv of imidoyl chlorides in the presence of triethylamine, thus producing the desired 2-acylaminopyridines in good yields (74-96%). 相似文献
316.
Analysis of herbicides in water using temperature-responsive chromatography and an aqueous mobile phase 总被引:1,自引:0,他引:1
Ayano E Okada Y Sakamoto C Kanazawa H Okano T Ando M Nishimura T 《Journal of chromatography. A》2005,1069(2):281-285
A simple and rapid method has been developed for herbicides in water using temperature-responsive liquid chromatography (LC) and a column packed with poly(N-isopropylacrylamide) (PNIPAAm), a polymer anchored on the stationary-phase surface of modified silica. PNIPAAm reversibly changes its hydrophilic/hydrophobic properties in water in response to temperature. The method was used to determine five sulfonylurea and three urea herbicides. Separation was achieved with a 10 mM ammonium acetate (pH 3.0) isocratic aqueous mobile phase, and by changing the column temperature. The analytes were extracted from water by off-line solid-phase extraction (SPE) with an N-vinyl-pyrrolidone polymer cartridge. The average recoveries of the eight herbicides from spiked pure water, tap water and river water were 70-130% with relative standard deviations (RSDs) of <10%. The limits of quantitation (LOQ) of the eight herbicides were between 1 and 4 microg l(-1). 相似文献
317.
Xiumei Chen Suguru Jinguu Suzuka Nishimura Yasunao Oyama Kazutaka Terashima 《Journal of Crystal Growth》2002,240(3-4):445-453
The density and the surface tension of molten calcium fluoride have been measured in the temperature range from 1690 to 1790 K by an improved Archimedian method and a ring depressing technique (J. Crystal Growth 187 (1998) 391), respectively. The ring depressing technique was demonstrated as an effective technique to measure the surface tension in comparison with the conventional ring pulling technique. The density varied with the temperature change corresponding to a linear relationship: ρ=3.767−6.94×10−4T (K). The density of the CaF2 melt at the melting point is 2.594 g/cm3, which is equal to the result obtained by Shiraishi and Watanabe (Bull. Res. Inst. Miner. Dressing Metal, Tohoku Univ. 34 (1978) 1), but the temperature coefficient of the density is different from the results obtained by other investigators. The thermal expansion coefficient of calcium fluoride melt linearly increases with temperature heating. The surface tension of molten calcium fluoride indicates a negative linear relationship as a function of the melt temperature: γ(T)=442.4−0.0816×T(K) (mN/m). The surface tension measured using the ring depressing technique is larger than those results obtained by other techniques. 相似文献
318.
J. Takada T. Sumino K. Nishimura Y. Tanaka K. Kawamoto M. Akaboshi 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(3):609-612
Since the rare earth elements (REE) are most informative as isomorphic replacements of Ca2+ in organisms, we analyzed these elements in 142 fern leaves collected from several sampling sites in Japan by instrumental
neutron activation analysis (INAA), and the correlation between the REE and Ca contents was examined. In most cases, between
any particular REE and the Ca contents, the correlation in the logarithmic scattering diagram was expressed as a single line
parallel to the vertical (Y) axis. However, the detailed analysis of the diagrams characterized with respect to the sampling
site revealed that the 142 ferns could be separated into two or three groups on the basis of their different REE/Ca ratios.
The sampling sites where the different REE/Ca ratios were observed completely agreed with those found in the preceding report,
i.e., regarding the unusual correlation between Eu and the other REEs.
The present work was supported in part by a Grant-in-Aid from the Ministry of Education, Science, Sports and Culture, Japan. 相似文献
319.
Kazumasa Ueda Toyonari Sugimoto Toshiji Tada Kei‐ichiro Nishimura Tomoyuki Mochida 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):400-402
In the tetramethylarsonium salt of 2,5‐dichloro‐7,7,8,8‐tetracyanoquinodimethanide [systematic name: tetramethylarsonium 2,2′‐(2,5‐dichlorocyclohexa‐2,5‐diene‐1,4‐diylidene)bis(propanedinitrile)], C4H12As+·C12H2Cl2N4? or [As(CH3)4](C12H2Cl2N4), the cation lies disordered about a twofold axis and the radical ion lies about an inversion center forming a uniform [interplanar distance 3.35 (2) Å] and one‐dimensional stacking without any slip. The electrical conductivity of the single crystal at room temperature was less than 10?9 S cm?1, and the temperature dependence of paramagnetic susceptibility obeyed a one‐dimensional antiferromagnetic Heisenberg model with a spin‐exchange integral of 83 K in the temperature range 1.8–320.0 K. 相似文献
320.
M. Yukawa Y. Watanabe Y. Nishimura Y. Guo Z. Yongru H. Lu W. Zhang L. Wei Z. Tao 《Analytical and bioanalytical chemistry》1999,363(8):760-766
This study was carried out for the determination of 238U and 232Th concentrations in soil and various foods obtained in high natural radiation areas in China for estimating the internal radiation doses caused by these radionuclides. Knowledge of the daily dietary intakes of the nuclides through foods is essential to evaluate the internal radiation dose. Several analytical methods were evaluated for their applicability and quality assurance. The accuracy and precision of ICP-MS is considerably better for determining trace elements like U and Th in fine powder samples. The estimated annual effective dose is 0.302 μ Sv/y for 238U and 1.86 μ Sv/y for 232Th in the high natural radiation area, and 0.0101 μ Sv/y for 238U and 0.177 μ Sv/y for 232Th in the control area. 相似文献