全文获取类型
收费全文 | 10462篇 |
免费 | 666篇 |
国内免费 | 440篇 |
专业分类
耳鼻咽喉 | 79篇 |
儿科学 | 156篇 |
妇产科学 | 136篇 |
基础医学 | 2271篇 |
口腔科学 | 111篇 |
临床医学 | 680篇 |
内科学 | 1941篇 |
皮肤病学 | 109篇 |
神经病学 | 812篇 |
特种医学 | 109篇 |
外科学 | 770篇 |
综合类 | 1194篇 |
预防医学 | 824篇 |
眼科学 | 63篇 |
药学 | 1502篇 |
中国医学 | 226篇 |
肿瘤学 | 585篇 |
出版年
2023年 | 88篇 |
2022年 | 193篇 |
2021年 | 272篇 |
2020年 | 190篇 |
2019年 | 154篇 |
2018年 | 178篇 |
2017年 | 209篇 |
2016年 | 257篇 |
2015年 | 298篇 |
2014年 | 540篇 |
2013年 | 640篇 |
2012年 | 517篇 |
2011年 | 614篇 |
2010年 | 564篇 |
2009年 | 610篇 |
2008年 | 678篇 |
2007年 | 592篇 |
2006年 | 583篇 |
2005年 | 531篇 |
2004年 | 455篇 |
2003年 | 339篇 |
2002年 | 305篇 |
2001年 | 261篇 |
2000年 | 199篇 |
1999年 | 216篇 |
1998年 | 183篇 |
1997年 | 192篇 |
1996年 | 142篇 |
1995年 | 164篇 |
1994年 | 142篇 |
1993年 | 138篇 |
1992年 | 90篇 |
1991年 | 96篇 |
1990年 | 98篇 |
1989年 | 88篇 |
1988年 | 80篇 |
1987年 | 67篇 |
1986年 | 49篇 |
1985年 | 88篇 |
1984年 | 70篇 |
1983年 | 43篇 |
1982年 | 37篇 |
1981年 | 46篇 |
1980年 | 32篇 |
1979年 | 41篇 |
1978年 | 30篇 |
1977年 | 39篇 |
1976年 | 18篇 |
1974年 | 18篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Interleukin-2 (IL-2), secreted principally by activated helper T-cells, plays a pivotal role in the generation and regulation
of the immune response. The various biologic functions of IL-2 have been the focus of intensive study over the years and have
been well worked out. By contrast, an understanding of the intracellular signals coupled to the IL-2 receptor and responsible
for mediating IL-2 effects in T-cells is far less developed, and the role that protein kinase C (PKC) may play in the various
cellular responses to IL-2 receptor activation is unclear. In this article we will discuss IL-2, its receptors, and IL-2 signal
transduction in relation to the physiological roles PKC activation may play in IL-2-mediated activation of T-cells and other
hematopoietic cells. 相似文献
92.
Nutritional studies on rats given a choice between two diets differing in protein content have led to the proposal that brain 5-HT content regulates protein intake [2]. Pharmacologic studies under similar conditions of dietary self-selection suggest that brain 5-HT controls carbohydrate intake [41]. We tested the effect of elevating brain 5-HT via tryptophan injection (100 mg/kg) on short-term food intake and selection by rats choosing between two diets differing in protein and carbohydrate content. Under these conditions neither total food intake nor protein and carbohydrate selection were affected despite increases of 50% in brain concentrations of 5-HT and 5-HIAA. The effect of Trp administration was selective to serotonin metabolism as brain concentrations of NE, DA and DOPAC were not affected. These results suggest that alterations in brain 5-HT content which may occur following meal ingestion may not be of physiological importance in regulating nutrient intake and selection. 相似文献
93.
中国版纳猪MHCI类P1分子全长的原核表达与纯化 总被引:8,自引:0,他引:8
目的:获得原核表达的中国版纳猪SLAI类P1蛋白质分子。方法:PCR扩增去信号肽的SLAI类P1cDNA序列,亚克隆至pGEMT载体,测序。将亚克隆的P1 cDNA片段插入表达载体pET42b(+),构建重组表达质粒pET-42b(+)/sla-pl,转化E·coli表达菌 BL21-CodonPlus(DE3)-RIL,IPTG诱导 P1-8 x his融合蛋白表达,经包涵体洗涤,8 mol/L尿素变性溶解,Ni2+亲和层析,梯度透析后,定量保存。SDS-PAGE、western-blotting鉴定目的蛋白的表达与纯化。结果:目的蛋白(分子量39.5 kD)表达量占细菌总蛋白 15%,每升表达菌获得纯度95%的目的蛋白 40 mg~60mg。结论:成功建立猪 SLA分子全长原核表达、纯化体系,为建立间接识别猪移植抗原SLAI类分子的人T细胞系及表位分析打下基础。 相似文献
94.
目的:探讨蛋白激酶C (PKC) 在大鼠脊髓背角C-纤维诱发电位长时程增强(LTP)的诱导和维持中的作用。方法: 细胞外记录技术在脊髓腰膨大部记录背角浅层神经元C-纤维诱发电位。 结果:(1) PKC的选择性抑制剂chelerythrine(200 μmol/L)或G 6983(100 μmol/L)对脊髓背角C-纤维诱发电位的基础电位没有影响,但可完全阻断脊髓背角LTP的诱导。(2) Chelerythrine或G 6983呈时间依赖性翻转脊髓背角LTP。在LTP 诱导后15 min,脊髓局部给予chelerythrine(200 μmol/L)后,LTP逐渐降低,于给药后70 min降至对照水平;而G 6983(100 μmol/L)产生同chelerythrine相似的效应,在用药后110 min,LTP降至对照水平。但同样浓度的chelerythrine或G 6983在LTP 诱导后3 h,均不能翻转业已建立的LTP。结论: PKC参与脊髓背角C-纤维诱发电位LTP的诱导和早期维持,而不影响晚期LTP的维持。 相似文献
95.
运用灰色系统理论中的 T型关联度分析方法 ,对类金刚石 (DL C)薄膜、富石墨相 DL C薄膜和富金刚石相 DL C薄膜三种 DL C薄膜进行了碳相成分对其白蛋白 (HSA)、纤维蛋白原 (HFG)、免疫球蛋白 (Ig G)三种血浆蛋白吸附量影响的定量分析研究。合理地解释了三种材料蛋白吸附量随碳相成分变化的实验结果 ,并得出如下重要的分析结论 :(1)石墨和 C- H相对 HSA的吸附影响较大 ,随着二者的增加 ,HSA的吸附量下降 ;(2 )与 HFG吸附有较强关联的碳相成分是 DL C相和 C- O相 ,前者呈负相关 ,后者为正相关 ;(3)各碳相成分对 Ig G的吸附均有性质不尽相同的影响 ,但程度有限 ,且彼此间相差不大 ;(4 ) DL C碳相具有增强 HSA吸附、抑制 HFG、Ig G吸附的双重功效 ,其对 DL C薄膜血液相容性的影响远较其它碳相成分更为重要。 相似文献
96.
The influence of internal Ca2+ ions has been investigated during intracellular perfusion of isolated neurones from pedal ganglia of Helix pomatia in which serotonin (5-HT) induces a cyclic-adenosine-monophosphate-(cAMP)-dependent enhancement of high-threshold Ca2+ current (I
Ca). Internal free Ca2+ ([Ca2+]i) was varied between 0.01 and 10 M by addition of Ca2+-EGTA [ethylenebis(oxonitrilo)tetraacetate] buffer. Elevation of [Ca2+]i depressed the 5-HT effect. The dose/ effect curve for the Ca2+ blockade had a biphasic character and could be described by the sum of two Langmuir's isotherms for tetramolecular binding with dissociation constants K
d1=0.063 M and K
d2=1 M. Addition of calmodulin (CM) antagonists (50 M trifluoperazine or 50 M chlorpromazine), phosphodiesterase (PDE) antagonists [100 M isobutylmethylxanthine (IBMX) or 5 mM theophylline] and protein phosphatase antagonists [2 M okadaic acid (OA)] in the perfusion solution caused anticalcium action and modified the Ca2+ binding isotherm. Using the effect of OA and IBMX, two components of the total Ca2+ inhibition were separated and evaluated. In the presence of one of these blockers tetramolecular curves with K
d1=0.04 M and K
d2=0.69 M were obtained describing the activation of the retained unblocked enzyme — PDE or calcineurin (CN) correspondingly. The sum of these isotherms gave a biphasic curve similar to that in control. Leupeptin (100 M), a blocker of Ca2+-dependent proteases did not influence the amplitude of 5-HT effect, indicating that channel proteolysis is not involved in the depression. Our findings show that the molecular mechanism of Ca2+-induced suppression of the cAMP-dependent upregulation of Ca2+ channels is due to involvement of two Ca2+-CM-dependent enzymes: PDE reducing the cAMP level, and CN causing channel dephosphorylation. No other processes are involved in the investigated phenomenon at a Ca2+ concentration of less than or equal to 10 M. 相似文献
97.
Crowding can substantially affect the transition of a protein between its native (N) and unfolded (U) states via volume exclusion
effects. Also, it influences considerably the aggregation (A) of unfolded proteins. To examine the details, we developed an
approach for computing the kinetic rates of the process N ↔ U → A in which the concentration of the protein is explicitly
taken into account. We then compute the relative change with temperature of the protein denaturation for various fractional
volume occupancies and partition of proteins in solution. The analysis indicates that, in protein solutions in which the average
distance between proteins is comparable with the radius of gyration of an unfolded protein, steric effects increase the stability
of the proteins which are in compact, native states. In heterogeneous protein solutions containing various types of proteins
with different thermal stabilities, the unfolding of the most thermolabile proteins will increase the stability of the other
proteins. The results shed light on the way proteins change the thermal stability of a cell as they unfold and aggregate.
This study may be valuable in questions related to the dynamics of thermal injuries. 相似文献
98.
Irene Held I. James Young 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1969,8(2):150-162
Summary After 3H-lysine was applied to the Xth and XIIth cranial nuclei, radioactive protein synthesized in the nerve cell bodies of the hypoglossal and vagus nerves moved down the axons of these fibers at maximal rates of 6.3±1.2 and 16±3 mm per day, respectively. The distribution of radiolabeled protein at various periods indicated that other proteinaceous components moved at slower velocities. 相似文献
99.
Summary A formula relating oncotic pressure torat serum protein concentration was derived and found to be in complete agreement with the Landis-Pappenheimer formula derived from measurements onhuman plasma.This study was supported by the Danish Medical Research Council and Johan and Hanne Weimann's legacy. 相似文献
100.
Leslie C. Grammer Loui Silvestri Irena M. Suszko Martha A. Shaughnessy Roy Patterson 《The Journal of allergy and clinical immunology》1983,72(2):160-167
The standardization procedures for polymerized ragweed (PRW) must evaluate activity of PRW with assessments that differ from those used for standard unmodified extracts. This is because PRW allergens are different from conventional ragweed extracts in that they are much greater in average molecular weight and much lower in allergenicity for equivalent immunogenicity. We have evaluated seven samples of PRW for three parameters: allergenicity as determined by cutaneous end point titration, molecular weight distribution as determined by Sephadex G-200 chromatography, and availability of antigen E (AgE) determinants as measured by the ability of an extract to inhibit AgE binding to antibody by using a modification of the Farr technique. The skin test titers and molecular weight profiles provide information as to the safety of a PRW preparation and antigen-binding inhibitory activity gives information about allergenicity and immunogenicity. Appropriate limits may be set for each of these parameters to standardize PRW for clinical use. 相似文献