全文获取类型
收费全文 | 1902269篇 |
免费 | 152024篇 |
国内免费 | 7180篇 |
专业分类
耳鼻咽喉 | 24379篇 |
儿科学 | 61961篇 |
妇产科学 | 50814篇 |
基础医学 | 272212篇 |
口腔科学 | 53111篇 |
临床医学 | 172299篇 |
内科学 | 381807篇 |
皮肤病学 | 44887篇 |
神经病学 | 149654篇 |
特种医学 | 75845篇 |
外国民族医学 | 346篇 |
外科学 | 293721篇 |
综合类 | 43669篇 |
现状与发展 | 4篇 |
一般理论 | 560篇 |
预防医学 | 148860篇 |
眼科学 | 41853篇 |
药学 | 137613篇 |
8篇 | |
中国医学 | 4274篇 |
肿瘤学 | 103596篇 |
出版年
2018年 | 19595篇 |
2017年 | 15372篇 |
2016年 | 18044篇 |
2015年 | 20107篇 |
2014年 | 27881篇 |
2013年 | 41990篇 |
2012年 | 52614篇 |
2011年 | 56164篇 |
2010年 | 34536篇 |
2009年 | 33394篇 |
2008年 | 52476篇 |
2007年 | 56092篇 |
2006年 | 57303篇 |
2005年 | 54875篇 |
2004年 | 52944篇 |
2003年 | 51027篇 |
2002年 | 48871篇 |
2001年 | 93679篇 |
2000年 | 96007篇 |
1999年 | 79886篇 |
1998年 | 22921篇 |
1997年 | 20203篇 |
1996年 | 21191篇 |
1995年 | 21118篇 |
1994年 | 19664篇 |
1993年 | 18300篇 |
1992年 | 65053篇 |
1991年 | 63726篇 |
1990年 | 61603篇 |
1989年 | 59395篇 |
1988年 | 54758篇 |
1987年 | 53630篇 |
1986年 | 50669篇 |
1985年 | 48469篇 |
1984年 | 36526篇 |
1983年 | 30780篇 |
1982年 | 18541篇 |
1981年 | 16669篇 |
1980年 | 15762篇 |
1979年 | 32996篇 |
1978年 | 23722篇 |
1977年 | 20026篇 |
1976年 | 18668篇 |
1975年 | 19821篇 |
1974年 | 23277篇 |
1973年 | 22259篇 |
1972年 | 20698篇 |
1971年 | 19133篇 |
1970年 | 17768篇 |
1969年 | 16551篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
971.
R D Verhalen 《Journal of urban health》1988,64(7):804-809
972.
973.
974.
975.
Investigation of Role of Nitric Oxide in Protection from Bordetella pertussis Respiratory Challenge 下载免费PDF全文
The mechanism whereby whole-cell pertussis vaccines (WCV) confer protection against Bordetella pertussis is still not fully understood. We have previously reported that macrophage activation produced by vaccination with WCV is associated with induction of NO synthesis by macrophages in response to in vitro stimulation with B. pertussis antigens. To determine whether NO production is an effector of protection or simply a marker of activation, the susceptibility of inducible nitric oxide synthase (type II, iNOS) knockout mice to infection with B. pertussis was examined. We showed that iNOS knockout mice were more susceptible to B. pertussis respiratory challenge than wild-type mice. iNOS-deficient mice also developed a less effective protective response than wild-type mice after the same immunization with WCV. This suggests that NO plays an important role in effecting protection against B. pertussis challenge. 相似文献
976.
Human balancing of an inverted pendulum: position control by small, ballistic-like, throw and catch movements 总被引:12,自引:4,他引:8
In standing, there are small sways of the body. Our interest is to use an artificial task to illuminate the mechanisms underlying the sways and to account for changes in their size. Using the ankle musculature, subjects balanced a large inverted pendulum. The equilibrium of the pendulum is unstable and quasi-regular sway was observed like that in quiet standing. By giving full attention to minimising sway subjects could systematically reduce pendulum movement. The pendulum position, the torque generated at each ankle and the soleus and tibialis anterior EMGs were recorded. Explanations about how the human inverted pendulum is balanced usually ignore the fact that balance is maintained over a range of angles and not just at one angle. Any resting equilibrium position of the pendulum is unstable and in practice temporary; movement to a different resting equilibrium position can only be accomplished by a biphasic 'throw and catch' pattern of torque and not by an elastic mechanism. Results showed that balance was achieved by the constant repetition of a neurally generated ballistic-like biphasic pattern of torque which can control both position and sway size. A decomposition technique revealed that there was a substantial contribution to changes in torque from intrinsic mechanical ankle stiffness; however, by itself this was insufficient to maintain balance or to control position. Minimisation of sway size was caused by improvement in the accuracy of the anticipatory torque impulses. We hypothesise that examination of centre of mass and centre of pressure data for quiet standing will duplicate these results. 相似文献
977.
978.
D. Lothschütz M. Jennewein S. Pahl H.F. Lausberg A. Eichler W. Mutschler R.G. Hanselmann M. Oberringer 《Inflammation research》2002,51(8):416-422
OBJECTIVE AND DESIGN: Inflammatory and tumorous bronchi were screened in order to obtain new tumor relevant cytogenetic parameters. MATERIAL OR SUBJECTS: Bronchial cells of 32 patients were cultivated by standard cell culture procedures. METHODS: Tetraploidy and aneuploidy was determined by enumeration of chromosome 7 and 8 versus the number of centrosomes. The resulting data were correlated with histopathological data. RESULTS: Tetra- and aneuploidy of epithelial cells were detectable in 76% of tumor cell cultures, 75% of high grade inflammatory tissues and 40% of non- and low grade-inflammatory tissues. Additionally, we observed centrosome hyper-amplification and multipolar mitoses not only in the tumor but also in the early stages of inflammation. CONCLUSION: Inflammatory bronchi already show tumor-specific features and may consequently represent the preliminary genetic stage of cancer development in bronchi. 相似文献
979.
OBJECTIVE: To assess the effect of the residual stresses due to cement curing on the load transfer of cemented hip implants. DESIGN: The load transfer at the stem-cement interface of an idealized hip stem surrounded by cortical bone was investigated using a three-dimensional finite element analysis. A debonded stem-cement interface was considered to simulate a highly polished stem in contact with cement; Coulomb friction at the stem-cement interface was considered. BACKGROUND: Numerical analyses on the load transfer of cemented hip implants do not include residual stresses due to cement curing at the stem-cement interface. METHODS: The magnitude of the residual stresses was determined experimentally. In the finite element model, non-linear contact elements modelled the debonded stem-cement interface. In particular, the compressive radial residual stresses that are generated at the interface, due to the cement expansion during curing, were treated similar to a press-fit problem. RESULTS: The cement stress distributions were affected by the magnitude of the residual stresses. Failing to include residual stresses underestimated the cement stresses at the interface, mainly affecting the radial and hoop stresses. The load was transferred from the stem to the cement more uniformly along the interface once residual stresses were included. CONCLUSIONS: Because there is no chemical bond at the interface between the stem and cement, the interface resistance depends on friction thus radial residual compressive stresses developed by the cement curing play a direct role. RELEVANCE: Implant loosening of cemented hip implants is one of the major causes of late failure of the arthroplasty. The load is transferred from the stem to the bone primarily across the interfaces, consequently modelling accurately the interface is essential in predicting the load transfer. 相似文献
980.
Characterization of the cross-bridge force-generating step using inorganic phosphate and BDM in myofibrils from rabbit skeletal muscles 总被引:10,自引:3,他引:7
The inhibitory effects of inorganic phosphate (Pi ) on isometric force in striated muscle suggest that in the ATPase reaction Pi release is coupled to force generation. Whether Pi release and the power stroke are synchronous events or force is generated by an isomerization of the quaternary complex of actomyosin and ATPase products (AM.ADP.Pi ) prior to the following release of Pi is still controversial. Examination of the dependence of isometric force on [Pi ] in rabbit fast (psoas; 5-15 °C) and slow (soleus; 15-20 °C) myofibrils was used to test the two-step hypothesis of force generation and Pi release. Hyperbolic fits of force-[Pi ] relations obtained in fast and slow myofibrils at 15 °C produced an apparent asymptote as [Pi ]∞ of 0.07 and 0.44 maximal isometric force (i.e. force in the absence of Pi ) in psoas and soleus myofibrils, respectively, with an apparent K d of 4.3 m m in both. In each muscle type, the force-[Pi ] relation was independent of temperature. However, 2,3-butanedione 2-monoxime (BDM) decreased the apparent asymptote of force in both muscle types, as expected from its inhibition of the force-generating isomerization. These data lend strong support to models of cross-bridge action in which force is produced by an isomerization of the AM.ADP.Pi complex immediately preceding the Pi release step. 相似文献