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排序方式: 共有749条查询结果,搜索用时 500 毫秒
741.
Shevela D Koroidov S Najafpour MM Messinger J Kurz P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(19):5415-5423
Oxygen evolution catalysed by calcium manganese and manganese-only oxides was studied in (18)O-enriched water. Using membrane-inlet mass spectrometry, we monitored the formation of the different O(2) isotopologues (16)O(2), (16)O(18)O and (18)O(2) in such reactions simultaneously with good time resolution. From the analysis of the data, we conclude that entirely different pathways of dioxygen formation catalysis exist for reactions involving hydrogen peroxide (H(2)O(2)), hydrogen persulfate (HSO(5)(-)) or single-electron oxidants such as Ce(IV) and [Ru(III) (bipy)(3)](3+) . Like the studied oxide catalysts, the active sites of manganese catalase and the oxygen-evolving complex (OEC) of photosystem II (PSII) consist of μ-oxido manganese or μ-oxido calcium manganese sites. The studied processes show very similar (18)O-labelling behaviour to the natural enzymes and are therefore interesting model systems for in vivo oxygen formation by manganese metalloenzymes such as PSII. 相似文献
742.
Geometrical structures,vibrational frequencies,force constants and dissociation energies of isotopic water molecules (H2O,HDO, D2O,HTO, DTO,and T2O) under dipole electric field
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The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H-O increases whereas the bond angle of H-O-H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields. 相似文献
743.
Isotopic production cross sections of fragmentation residues produced by 18O ions on a carbon target near 260 MeV/nucleon
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Xiao-Dong Xu Ya-Zhou Sun Shi-Tao Wang Bo Mei Shu-Ya Jin Xue-Heng Zhang Zhi-Yu Sun Yi-Xuan Zhao Shu-Wen Tang Yu-Hong Yu Duo Yan Fang Fang Yong-Jie Zhang Shao-Bo Ma 《中国物理C(英文版)》2022,46(11):111001-111001-6
The isotopic cross sections of residual nuclei produced in fragmentation reactions of 18O projectiles impinging on a carbon target at energies near 260 MeV/nucleon were measured at the HIRFL facility in Lanzhou (China). A full identification of atomic and mass numbers of fragments was achieved from the determination of their magnetic rigidity, energy loss, and time of flight. The production cross sections for a dozen of nitrogen, carbon, and boron isotopes were determined with uncertainties below 30% for most of the cases. The obtained cross sections for N and B isotopes show a rather good agreement with previous experimental data obtained with different projectile energies. The cross sections for some C isotopes seem to exhibit a dependence on the projectile energy. A comparison of the data and several theoretical model calculations are presented. 相似文献
744.
745.
PURPOSE: To identify regional arterial input functions (AIFs) using factor analysis of dynamic studies (FADS) when quantification of perfusion is performed using model-free arterial spin labelling. MATERIAL AND METHODS: Five healthy volunteers and one patient were examined on a 3-T Philips unit using quantitative STAR labelling of arterial regions (QUASAR). Two sets of images were retrieved, one where the arterial signal had been crushed and another where it was retained. FADS was applied to the arterial signal curves to acquire the AIFs. Perfusion maps were obtained using block-circulant SVD deconvolution and regional AIFs obtained by FADS. In the volunteers, the ASL experiment was repeated within 24 h. The patient was also examined using dynamic susceptibility contrast MRI. RESULTS: In the healthy volunteers, CBF was 64+/-10 ml/[min 100 g] (mean+/-S.D.) in GM and 24+/-4 ml/[min 100 g] in WM, while the mean aBV was 0.94% in GM and 0.25% in WM. DISCUSSION: Good CBF image quality and reasonable quantitative CBF values were obtained using the combined QUASAR/FADS technique. We conclude that FADS may be a useful supplement in the evaluation of ASL data using QUASAR. 相似文献
746.
��־ǿ���Է���� �ܣ��κ�����˻���������뿪�� 《核聚变与等离子体物理》2018,38(3):344-349
研究了低活化马氏体钢(CLF-1)热等静压(HIP)焊接接头的性能,经980℃/1h/空冷+740℃/2h/空冷的性能热处理后,接头组织保持着CLF-1钢母材回火马氏体组织;常温拉伸性能与母材相当,断口为韧窝状且有第二相粒子产生,为塑性断裂且断于焊缝;常温冲击功最高为母材的26.2%。初步分析认为焊接表面制备状态、表面污染物、表面清洗状态、表面氧化膜都会影响基体原子充分扩散,导致界面扩散层不均匀,焊缝裂纹敏感性增强,冲击功低,且不稳定。 相似文献
747.
When N‐benzyl‐N′‐methylacetamidinium hydrochloride (pKa=11.8) is dissolved in D2O/DCl(1 M), an equilibrium of 2 54:46 stereoisomers in an ~2:1 =(R)Nδ+H(D) D/H ratio is formed. Therefore, 2 R =N‐benzyl (E and Z) and 2 R =N‐methyl (E and Z) groups attached to the corresponding H(D) (Z and E) for a total of 8 1H‐NMR signals are observed. Consequently, their rates of H and D transfer to D2O can be measured by means of the 1H‐NMR broadness (line shape) of the =(R )Nδ+H doublets and =(R )Nδ+D broad singlets. Acidity selectivity is observed for both processes. In fact, the relative proton and deuterium transfer rates follow the acidity order: =(PhCH2)Nδ+‐H(E) > =(PhCH2)Nδ+‐H(Z) > =(Me)Nδ+‐H(E) > =(Me)Nδ+‐H(Z). Proton transfer rates are in the range of 8 to 0.5 s‐1 with α = .92. This tendency is independently supported by the observed experimental chemical shift deuterium isotopic perturbation. The rate‐limiting step for proton exchange is the breaking of the hydrogen bond due to the fast amidine reprotonation (~1011 s). =(R)Nδ+D/=(R)Nδ+H equilibration is reached at ~80 s, and it can be measured by the relative =(R) Nδ+H versus =(R) Nδ+D signal integrations. The equilibrium of the 4 =(R)Nδ+H(D) centers is shifted toward deuterium, but they are further shifted in the more basic centers. Equilibrium is completely shifted toward D in the 4 centers when OD? contributes with the exchange process at pD > 3. 相似文献
748.
Tran Thu Huong Le Thi Vinh Hoang Thi Khuyen Le Dac Tuyen Nguyen Duc Van Do Thi Thao Ha Thi Phuong 《Molecules (Basel, Switzerland)》2023,28(1)
We present a visual tool and facile method to detect MCF-7 breast cancer cells by using YVO4:Eu3+@silica-NH-GDA-IgG bio-nanocomplexes. To obtain these complexes, YVO4:Eu3+ nanoparticles with a uniform size of 10–25 nm have been prepared firstly by the hydrothermal process, followed by surface functionalization to be bio-compatible and conjugated with cancer cells. The YVO4:Eu3+@silica-NH-GDA-IgG nanoparticles exhibited an enhanced red emission at 618 nm under an excitation wavelength of 355 nm and were strongly coupled with MCF-7 breast cancer cells via biological conjugation. These bio-nanocomplexes showed a superior sensitiveness for MCF-7 cancer cell labelling with a detection percentage as high as 82%, while no HEK-293A healthy cells were probed under the same conditions of in vitro experiments. In addition, the detection percentage of MCF-7 breast cancer cells increased significantly via the functionalization and conjugation of YVO4:Eu3+ nanoparticles. The experimental results demonstrated that the YVO4:Eu3+@silica-NH-GDA-IgG bio-nanocomplexes can be used as a promising labelling agent for biomedical imaging and diagnostics. 相似文献
749.
Maaret Toiviala Vesa Kleemola Sajal Maity Tuomas Lönnberg 《European journal of organic chemistry》2023,26(10):e202201443
Both α and β anomers of an acetophenone C-nucleoside were synthesized and incorporated in the middle of short oligodeoxynucleotides. The ketone oligonucleotides were converted to 15N-labelled oxime oligonucleotides by treatment with 15N-hydroxylamine and, finally, cyclopalladated by treatment with lithium tetrachloropalladate. Comparison of the UV melting profiles of duplexes bearing the β anomer of either the palladacyclic or the metal-free oxime C-nucleoside suggested formation of a stable Pd(II)-mediated base pair, especially with adenine or thymine as the base pairing partner. Melting profiles of the corresponding duplexes bearing the α anomer were much more convoluted, precluding meaningful comparison. 15N NMR spectra were obtained for the β anomeric oxime oligonucleotide as well as its palladacyclic derivative but the signals unfortunately diminished below detection limit when the latter was hybridized with a complementary strand placing a 15N3-labelled thymine opposite to the palladacyclic residue. 相似文献