全文获取类型
收费全文 | 72773篇 |
免费 | 5740篇 |
国内免费 | 4707篇 |
专业分类
化学 | 28075篇 |
晶体学 | 187篇 |
力学 | 3790篇 |
综合类 | 1258篇 |
数学 | 31507篇 |
物理学 | 18403篇 |
出版年
2023年 | 623篇 |
2022年 | 883篇 |
2021年 | 2107篇 |
2020年 | 1540篇 |
2019年 | 1653篇 |
2018年 | 1318篇 |
2017年 | 1561篇 |
2016年 | 2035篇 |
2015年 | 1833篇 |
2014年 | 2960篇 |
2013年 | 4686篇 |
2012年 | 3171篇 |
2011年 | 3703篇 |
2010年 | 3367篇 |
2009年 | 4360篇 |
2008年 | 4585篇 |
2007年 | 4805篇 |
2006年 | 3882篇 |
2005年 | 3024篇 |
2004年 | 2606篇 |
2003年 | 2646篇 |
2002年 | 4912篇 |
2001年 | 2422篇 |
2000年 | 1962篇 |
1999年 | 1677篇 |
1998年 | 1606篇 |
1997年 | 1288篇 |
1996年 | 1127篇 |
1995年 | 948篇 |
1994年 | 917篇 |
1993年 | 859篇 |
1992年 | 810篇 |
1991年 | 550篇 |
1990年 | 470篇 |
1989年 | 386篇 |
1988年 | 425篇 |
1987年 | 339篇 |
1986年 | 343篇 |
1985年 | 511篇 |
1984年 | 397篇 |
1983年 | 216篇 |
1982年 | 421篇 |
1981年 | 582篇 |
1980年 | 515篇 |
1979年 | 539篇 |
1978年 | 432篇 |
1977年 | 336篇 |
1976年 | 299篇 |
1974年 | 94篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Most of the novel highly potent drugs, developed on the basis of modern molecular medicine, taking into account cell surface recognition techniques, show poor water solubility. A chemical modification of the drug substance enhancing the solubility often decreases the pharmacological activity. Thus, as an alternative an increase of the solubility can be obtained by the reduction of the size of the drug particles. Unfortunately, it is often difficult to obtain micro or nanosized drug particles by classical or more advanced crystallization using supercritical gases or by milling techniques. In addition, nanosized particles are often not physically stable and need to be stabilized in an appropriate matrix. Thus, it may be of interest to manufacture directly nanosized drug particles stabilized in an inert hydrophilic matrix, i.e. nanostructured and nanocomposite systems. Solid solutions and solid dispersions represent nanostructured and nanocomposite systems. In this context, the use of the vacuum-fluidized-bed technique for the spray-drying of a low water soluble drug cosolubilized with a hydrophilic excipient in a polar organic solvent is discussed. In order to avoid the use of organic solvents, a special spray-freeze-drying technique working at atmospheric pressure is presented. This process is very suitable for temperature and otherwise sensitive drugs such as pharmaproteins. 相似文献
82.
83.
A. Mielke 《Journal of statistical physics》1991,62(3-4):509-528
The magnetic properties of the one-dimensional Hubbard model with a hardcore interaction on a ring (periodic boundary conditions) are investigated. At finite temperatures it is shown to behave up to exponentially small corrections as a pure paramagnet. An explicit expression for the ground-state degeneracies is derived. The eigenstates of this model are used to perform a perlurbational treatment for large but finite interactions. In first order inU
1 an effective Hamiltonian for the one-dimensional Hubbard model is derived. It is the Hamiltonian of the one-dimensional Hcisenberg model with antiferromagnetic couplings between nearest neighbor spins. An asymptotic expansion for the ground-state energy is given. The results are valid for arbitrary densities of electrons. 相似文献
84.
We describe a new algorithm which uses the trajectories of a discrete dynamical system to sample the domain of an unconstrained objective function in search of global minima. The algorithm is unusually adept at avoiding nonoptimal local minima and successfully converging to a global minimum. Trajectories generated by the algorithm for objective functions with many local minima exhibit chaotic behavior, in the sense that they are extremely sensitive to changes in initial conditions and system parameters. In this context, chaos seems to have a beneficial effect: failure to converge to a global minimum from a given initial point can often be rectified by making arbitrarily small changes in the system parameters. 相似文献
85.
对红外热像仪参数双黑体测量装置的工作原理进行了介绍。装置采用双黑体及反射型靶标为温差辐射源,可实现黑体温度温差准直辐射的定期校准和红外热像仪参数测量量值的溯源,也可实现红外热像仪参数的可控性,以及对它进行稳定的、可复现的精确测量。推导出利用红外热像仪参数双黑体测量装置测量信号传递函数SiTF数学模型,分析了红外热像仪参数测量装置的客观因素——仪器常数,针对仪器常数对SiTF测量的影响进行了试验。试验结果表明,仪器常数对红外热像仪SiTF参数测量精度影响较大,并同时影响时域与空域NETD及3D噪声的准确测量。 相似文献
86.
87.
ZHANG Shibin ZHANG Xinsheng & SUN Shuguang School of Management Fudan University Shanghai China Department of Mathematics Shanghai Maritime University Shanghai China 《中国科学A辑(英文版)》2006,49(9):1231-1257
The stationary Gamma-OU processes are recommended to be the volatility of the financial assets. A parametric estimation for the Gamma-OU processes based on the discrete observations is considered in this paper. The estimator of an intensity parameter A and its convergence result are given, and the simulations show that the estimation is quite accurate. Assuming that the parameter A is estimated, the maximum likelihood estimation of shape parameter c and scale parameter a, whose likelihood function is not explicitly computable, is considered. By means of the Gaver-Stehfest algorithm, we construct an explicit sequence of approximations to the likelihood function and show that it converges the true (but unkown) one. Maximizing the sequence results in an estimator that converges to the true maximum likelihood estimator and the approximation shares the asymptotic properties of the true maximum likelihood estimator. Some simulation experiments reveal that this method is still quite accurate in most of rational situations for the background of volatility. 相似文献
88.
两种拔尿管方法对膀胱功能损伤的临床观察 总被引:2,自引:0,他引:2
为观察两种不同的拔尿管方法对膀胱功能损伤的差异,将80例患者随机分成两组,分别采用改良法(40例)和常规法(40例)拔除留置尿管,分析比较了两组患者排尿顺利率、逼尿肌功能恢复率及尿道刺激症、尿失禁、尿潴留。结果表明,两组患者拔管后上述指标与情况有显著性差异,P<0.05。提示改良组膀胱功能损伤明显低于对照组。改良的拔管方法是一种值得护理推广应用的好方法。 相似文献
89.
设 $\varphi$ 是单位园盘 $D$ 到自身的解析映射, $X$ 是 $D$ 上解析函数的 Banach 空间, 对 $f\in X$, 定义复合算子$C_\varphi $ : $C_\varphi (f)=f\circ \varphi$. 我们利用从 ${\cal B}^0$到 $E(p,q)$ 和 $E_0(p,q)$ 空间的复合算子研究了空间 $E(p,q)$ 和 $E_0(p,q)$, 给出了一个新的特征. 相似文献
90.
本文指出 M.Jahangiri的评论[Mathematical Reviews 98e:30020]错误,并且导出解析函数p叶星形性与p叶凸性的某些充分条件. 相似文献