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31.
Crystals of L-leucylglycylglycylglycine, LGGG (C12H22N4O5), grown from an ethanol-water solution, are orthorhombic, space groups P212121, with unit cell dimensions (at 22 ± 3°) a = 9.337(1), b = 10.995(1), c = 15.235(1)Å, v = 1563.4 Å3, Z = 4 with a density of Dobs= 1.29 g-cm-3 and Dcalc= 1.279 g°cm-3. The crystal structure was solved by the application of direct methods and refined to an R value of 0.029 for 1018 reflections with I ± 2s?. The molecule exists as a zwitterion in the crystal. The trans peptide backbone takes up a folded conformation at the middle glycylglycyl link accompanied by a significant nonplanarity up to Δω of 8° at the middle peptide and is relatively more extended at the two ends. The molecules are linked together intermolecularly in an infinite sequence of head to tail 1–4′ hydrogen bonds, as is typical of charged peptides. It is interesting to note that while glycylglycylglycine takes up an extended β-sheet conformation, addition of Leu to the N-terminal results in a bent conformation. 相似文献
32.
Membrane flow within the myelin sheath in IDPN neuropathy 总被引:1,自引:0,他引:1
A. E. BLAUROCK M. B. GENTER ST CLAIR D. G. GRAHAM 《Neuropathology and applied neurobiology》1991,17(4):309-321
This report describes some aspects of beta,beta'-iminodipropionitrile (IDPN) neuropathy in rats as observed by ultrastructural methods and X-ray diffraction. Light microscopy shows gross swelling of the axons in proximal lumbar spinal roots 8 days after intraperitoneal injection of IDPN. Mean axon cross-sectional area and mean axon perimeter increased to 280% and 160% of their control values, respectively. At the same time, myelin membrane packing was not visibly disturbed. In addition, X-ray diffraction patterns, recorded under physiological conditions, demonstrate that the myelin lipid bilayer thickness and widths of the aqueous spaces between bilayers did not change. Related observations are made on posterior tibial nerve (PNS myelin) and ventral spinal cord (CNS myelin). The various observations together are interpreted in terms of a fluid myelin membrane. It is proposed that the myelin membrane flows during axon swelling even though normal membrane-membrane contacts are maintained within the sheath. Membrane flow and slippage between membranes are explained in terms of a molecular model of the myelin multilayer. 相似文献
33.
34.
人皮质骨矿化基质中骨盐框架结构 总被引:2,自引:0,他引:2
目的:研究人皮质骨矿化基质中骨盐的框架结构及框架中骨微间隙。方法:应用透射电镜、场发射扫描电镜观察、电脑图像分析及能谱分析,分析无骨病成人长骨、扁骨200例骨盐分布特征。结果:骨盐框架结构由微柱、微梁、微小梁、弓状梁、致密点、隔板和骨微间隙构成。骨微间隙由洞、内衬和壁组成,洞平均直径为84.4±75.6nm,与骨小管相比有显著差异(P值<0.001),平均密度为11~17个/μm2,与骨小管之比超过10:1。骨盐分针形结晶和微颗粒结晶。结论:骨盐框架结构及骨微间隙是骨盐在人皮质骨矿化基质中的存在形式,可能与骨盐吸收、沉着有关。 相似文献
35.
Objective: To study differences related to intensive care unit (ICU) structure and patient demography between the various countries
of Western Europe. Design: Application of data collected by the European Prevalence of Infection in Intensive Care (EPIC) study, a one-day prevalence
study. Setting: Voluntary participation of all Western European ICUs. A total of 1417 ICUs responded. Patients: All patients, older than 10 years of age, occupying a bed in the participating ICUs over a 24-h period. 10 038 patient case
reports were submitted. Results: The study revealed important differences. In particular, there seems to be a north/south divide with fewer ICU beds and more
severely ill patients in the south. The United Kingdom seemed more similar to southern European countries than to the north.
Conclusion: While there are similarities between European countries, large differences still remain and are important to identify to
enable us to work together to create a more uniform system of intensive care, which will in turn give more effective and efficient
patient care.
Received: 7 February 1997 Accepted 8 July 1997 相似文献
36.
用橡胶木粉填充线性低密度聚乙烯(LLDPE),研究了酸、碱溶液预处理木粉的效果和硅烷偶联荆(KH-570)、MMA接枝的天然橡胶胶乳(MGL-30)两种改性剂对橡胶木粉表面改性的效果,以及未粉粒径和填充量等对木粉/LLDPE复合材料力学性能的影响,并用SEM对复合材料拉伸断面的形态结构进行了分析。结果表明:木粉的拉径、木粉填充量和改性荆用量对复合材料的力学性能有较大的影响,经碱溶液预处理再用改性荆改性后的木粉能有效地改善木粉与LLDPE的界面粘结强度,提高橡胶木粉/LLDPE复合材料的力学性能。 相似文献
37.
为筛选大叶紫薇叶中具有降血糖活性的成分,采用3T3-L1细胞葡萄糖消耗模型作为检测手段,对大叶紫薇叶提取物采用HP-20树脂吸附、溶剂萃取、制备薄层分离和制备高效液相分离,导向筛选具有降血糖作用的各分离组分.结果发现,大叶紫薇叶中corosolic acid、熊果酸和总三萜具有降血糖活性. 相似文献
38.
LARBI EL-MASDOURI ANDR AUBRY GUY BOUSSARD MICHEL MARRAUD 《Chemical biology & drug design》1992,40(6):482-486
The similar conformations and interaction modes of Ac-DL-Leu-Nme2 and Ac-Δ-Leu-NMe2 molecules in the solid state allow the comparison of their geometrical parameters. The most evident variations are essentially restricted to the α,β-unsaturated side-chain which adopts the Z-disposition. The dimensions of the peptide backbone are much less sensitive to α,β-unsaturation, with a small shortening by 0.04 Å and 0.02 Å of the N-Cα and Cα-C′ bonds, respectively, and an increase by 6° of the N-Cα- C′ bond angle. The ethylenic and amide groups in the Δ-Leu derivative are far from coplanarity, and a significant electronic conjugation of the π-orbital is likely to be rejected. 相似文献
39.
The crystal structure of a tripeptide, tryptophanyl-glycyl-glycine dihydrate (C15H18N4O4·2H2O, molecular weight = 354) has been determined. The crystals are orthorhombic, space group P212121 with a= 7.875 (1) A,b= 9.009(1), c= 24.307(1) and Z = 4. The final R-index is 0.058 for 1488 reflections ((sin θ/λ≤ 0.6 A?1) with I < 2σ(I). The molecule exists as a zwitterion, with terminal NH+3 and COO? groups. The peptide units are trans and nearly perpendicular to the plane of the carboxyl group. The backbone torsion angles are: ψ1= 132.7°, ω1= 174.2°, φ2 88.2°, ψ= 8.6°, ω2 - 179.8°, φ= - 85.2°, ψ31, = - 178.1°, ψ32 5.0°. For the sidechain of tryptophan, χ1= - 171.6°, χ2 101.0°. 相似文献
40.
The dipeptide, L-prolyl-L-isoleucine monohydrate (C11 H20N2O3· H2O, molecular weight 246.3) crystallizes in the monoclinic space group P21, with a = 6.601(3)Å, b = 5.413(3) Å, c = 19.128(6) Å, β= 98.1(1)°, Z = 2, Do = 1.20g·cm-3 and Dc = 1.208g·cm-3. The structure was solved by MULTAN–80 and refined to a final R-factor of 0.081 for 594 reflections measured on a Enraf Nonius CAD-4 diffractometer. The peptide linkage exists in the trans conformation. The pyrrolidine ring is disordered with two alternate envelope conformations for the Cγ atom. The values of the sidechain torsion angles are: χ11=– 63.6(17)°, χ12= 171.1(16)° and χ2=– 59.6(21)° for isoleucine (C-terminal). The crystal structure is stabilized by a three-dimensional network of N—H ? O, O—H ? O and C—H ? O hydrogen bonds. The dipeptide exists in the extended Conformation. 相似文献