全文获取类型
收费全文 | 13972篇 |
免费 | 1062篇 |
国内免费 | 301篇 |
专业分类
耳鼻咽喉 | 106篇 |
儿科学 | 233篇 |
妇产科学 | 396篇 |
基础医学 | 1227篇 |
口腔科学 | 132篇 |
临床医学 | 1158篇 |
内科学 | 2029篇 |
皮肤病学 | 88篇 |
神经病学 | 898篇 |
特种医学 | 1201篇 |
外国民族医学 | 3篇 |
外科学 | 860篇 |
综合类 | 1725篇 |
预防医学 | 898篇 |
眼科学 | 83篇 |
药学 | 2427篇 |
12篇 | |
中国医学 | 695篇 |
肿瘤学 | 1164篇 |
出版年
2024年 | 34篇 |
2023年 | 211篇 |
2022年 | 554篇 |
2021年 | 676篇 |
2020年 | 488篇 |
2019年 | 422篇 |
2018年 | 412篇 |
2017年 | 469篇 |
2016年 | 568篇 |
2015年 | 537篇 |
2014年 | 837篇 |
2013年 | 850篇 |
2012年 | 810篇 |
2011年 | 754篇 |
2010年 | 713篇 |
2009年 | 585篇 |
2008年 | 633篇 |
2007年 | 649篇 |
2006年 | 537篇 |
2005年 | 478篇 |
2004年 | 446篇 |
2003年 | 446篇 |
2002年 | 369篇 |
2001年 | 347篇 |
2000年 | 265篇 |
1999年 | 235篇 |
1998年 | 182篇 |
1997年 | 179篇 |
1996年 | 139篇 |
1995年 | 135篇 |
1994年 | 134篇 |
1993年 | 108篇 |
1992年 | 127篇 |
1991年 | 142篇 |
1990年 | 141篇 |
1989年 | 82篇 |
1988年 | 91篇 |
1987年 | 82篇 |
1986年 | 58篇 |
1985年 | 59篇 |
1984年 | 60篇 |
1983年 | 46篇 |
1982年 | 50篇 |
1981年 | 40篇 |
1980年 | 40篇 |
1979年 | 31篇 |
1978年 | 19篇 |
1977年 | 11篇 |
1975年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
1.
2.
As a consequence of the time-varying magnetic field induced by eddy currents, frequency drifting occurs when the sampling window of localized spectroscopy continuously shifts. The frequency drifting and the concomitant phase variations can severely affect spectroscopy results when data are acquired with multiple echo times (TEs), such as in the measurement of glutamate (Glu) concentration using the TE-averaged method. Specifically, the averaged spectra are further broadened and distorted in the presence of residual eddy currents, and editing of the coupled spins of Glu C4 protons is affected, resulting in errors in the measured relative intensity ratio. Postacquisition correction using unsuppressed water as reference can effectively minimize this detrimental effect, as manifested by the significantly enhanced signal intensity. Also, it is demonstrated that the methyl signals of creatine (Cr) at 3.0 ppm and choline (Cho) at 3.2 ppm can be used as internal references in finding frequency and phase disparities between different TEs. 相似文献
3.
Carlo Bertucci Enrico Domenici Piero Salvadori 《Journal of pharmaceutical and biomedical analysis》1990,8(8-12):843-846
The application of a circular dichroism (c.d.) detection system in HPLC using a chiral stationary phase is presented. The simultaneous measurement of the absorbance and c.d. signal allows the evaluation of the anisotropy factor (g = Δ/) and thus the determination of the enantiomeric excess (e.e.) of the eluates. When this detection system is used in preparative chiral chromatography the collection of the enantiomeric fractions can be readily optimized. 相似文献
4.
5.
6.
S. Vemuri 《Chemical biology & drug design》2005,65(4):433-439
Abstract: Precise determination of the peptide content in drug substance samples depends highly upon the particular peptide compound and methodology used. Four independent methods were evaluated and compared to determine which would produce the best experimental precision for analysis of thymalfasin (thymosin α‐1). Four different methods were evaluated including elemental analysis (CHN), quantitative amino acid analysis (AAA), high‐performance liquid chromatography (HPLC), and Kjeldahl. This study demonstrates that the AAA method is highly variable in one laboratory while quite precise in another laboratory. Similarly, HPLC results depended on the laboratory conducting the study with more precise values obtained under cGMP. On the contrary, the CHN method yielded highly precise [i.e. <2% coefficient of variation (CV)] values. As precise knowledge of protein content is fundamental for the compounding of final pharmaceutical product of a specific potency, the CHN analysis is recommended for peptide content determination of the drug substance thymalfasin. 相似文献
7.
Teng-Yi Huang Hsiao-Wen Chung Fu-Nien Wang Cheng-Wen Ko Cheng-Yu Chen 《Magnetic resonance in medicine》2004,51(2):243-247
In this work the feasibility of separating fat and water signals using the balanced steady-state free precession (SSFP) technique is demonstrated. The technique is based on the observation (Scheffler and Hennig, Magnetic Resonance in Medicine 2003;49:395-397) that at the nominal values of TE = TR/2 in SSFP imaging, phase coherence can be achieved at essentially only two orientations (0 degrees and 180 degrees ) relative to the RF pulses in the rotating frame, under the assumption of TR < T2, and independently of the SSFP angle. This property allows in-phase and out-of-phase SSFP images to be obtained by proper choices of the center frequency offset, and thus allows the Dixon subtraction method to be utilized for effective fat-water separation. The TR and frequency offset for optimal fat-water separation are derived from theories. Experimental results from healthy subjects, using a 3.0 Tesla system, show that nearly complete fat suppression can be accomplished. 相似文献
8.
Phase II clinical trials are performed to investigate whether a novel treatment shows sufficient promise of efficacy to justify its evaluation in a subsequent definitive phase III trial, and they are often also used to select the dose to take forward. In this paper we discuss different design proposals for a phase II trial in which three active treatment doses and a placebo control are to be compared in terms of a single‐ordered categorical endpoint. The sample size requirements for one‐stage and two‐stage designs are derived, based on an approach similar to that of Dunnett. Detailed computations are prepared for an illustrative example concerning a study in stroke. Allowance for early stopping for futility is made. Simulations are used to verify that the specified type I error and power requirements are valid, despite certain approximations used in the derivation of sample size. The advantages and disadvantages of the different designs are discussed, and the scope for extending the approach to different forms of endpoint is considered. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
Response rates,duration of response,and dose response effects in phase I studies of antineoplastics 总被引:4,自引:0,他引:4
Summary Over a period of 14 years, 7,960 patients were treated in 228 phase I trials. In these patients, there were 75 complete and 432 partial responses for an overall objective response rate of 6%. Complete responses lasted a median of six months (range 1–18), while partial responses lasted a median of three months (range 1–17). Of note is that no drug has made it to the market which has not had a response in phase I trials. Responses were noted in very diverse histologic types of tumors. Although there were responses at doses which were as low as 3–5% of the recommended dose for phase II trials, the majority of responses did occur at 80–120% of the dose recommended for phase II trials. Although the response rate in phase I trials is indeed low, responses do occur. This response rate information should help the clinician provide facts for the patient considering a phase I trial with new anticancer agents. These findings also emphasize that although phase I trials are characteristically dose-finding studies, if no responses are noted in phase I studies, it is unlikely the drug will be used routinely in the clinic. 相似文献
10.
M L Cibull M E Thompson L Smith C D Jennings M A Doukas E J Pavlik D E Powell 《American journal of hematology》1987,24(3):293-299
The emergence of a near-haploid clone of cells in blast phase chronic myelogenous leukemia is an unusual event. We report such a case and review eight other cases described in the English literature. The significance of the substantial loss of genetic material is discussed as is the phenotypic and genotypic heterogeneity observed in this group of patients. 相似文献