全文获取类型
收费全文 | 1841篇 |
免费 | 66篇 |
国内免费 | 6篇 |
专业分类
化学 | 1341篇 |
晶体学 | 26篇 |
力学 | 44篇 |
数学 | 216篇 |
物理学 | 286篇 |
出版年
2023年 | 16篇 |
2022年 | 21篇 |
2021年 | 23篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 40篇 |
2015年 | 39篇 |
2014年 | 42篇 |
2013年 | 88篇 |
2012年 | 88篇 |
2011年 | 133篇 |
2010年 | 55篇 |
2009年 | 53篇 |
2008年 | 110篇 |
2007年 | 111篇 |
2006年 | 106篇 |
2005年 | 97篇 |
2004年 | 79篇 |
2003年 | 86篇 |
2002年 | 58篇 |
2001年 | 34篇 |
2000年 | 23篇 |
1999年 | 32篇 |
1998年 | 17篇 |
1997年 | 24篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 19篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 27篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 24篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 18篇 |
1974年 | 11篇 |
排序方式: 共有1913条查询结果,搜索用时 15 毫秒
1.
Cover Picture: Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands (Chem. Eur. J. 19/2015)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
2.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions. 相似文献
3.
Susan Baker Lisa Kelchner Barbara Weinrich Linda Lee Paul Willging Robin Cotton Karen Zur 《Journal of voice》2006,20(4):631-641
Laryngotracheal stenosis is defined as a congenital or acquired narrowing of the airway. Congenital causes may include subglottic membranous or cartilaginous narrowing. Acquired causes may include trauma due to prolonged endotracheal or tracheal intubation or laryngotracheal injury. Although advances have been made over the past 30 years in reconstructive surgeries to improve airway patency in these patients, long-term laryngeal function for voice production is not well defined in this population. This review examines causes, symptoms and signs, and methods for diagnosing laryngotracheal stenosis. Surgical management procedures are briefly summarized. The current literature on voice outcomes is summarized. The predominant voice characteristics in the population are presented, although results are challenged by the heterogeneity of voice presentation and paucity of data from instrumental measures. Considerations for subjective and instrumental assessment, measures of quality of life, instrumental methods, and treatment options specific to the needs of this population are discussed. Research strategies to identify long-term outcomes of surgical and behavioral treatments in this population are posed. 相似文献
4.
5.
Mark Doyle Susan A. Mulligan Tetsuya Matsuda Gerald M. Pohost 《Magnetic resonance imaging》1992,10(6):887-892
A new “bright blood” strategy, outflow refreshment imaging, is introduced in which a number of overlapping slices are excited in rapid succession. Flowing spins that refresh each overlapped slice portion contribute a bright signal. Additionally, static tissue in each non-overlapped slice portion also yields a bright signal. However, the flow/static contrast is comparable to that produced in inflow refreshment images, and angiograms can be generated by conventional maximum intensity projection processing. The dual ability to visualize angiograms and static tissue images is a major benefit of the strategy. Computer simulations of flow sensitivities and in vivo results are presented which compare the outflow and inflow refreshment imaging strategies. 相似文献
6.
7.
8.
Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings
The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO3 coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr LII, LIII-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant. 相似文献
9.
Peter G. Doyle Colin Mallows Alon Orlitsky Larry Shepp 《Israel Journal of Mathematics》1989,67(1):34-42
Letn cells be arranged in a ring, or alternatively, in a row. Initially, all cells are unmarked. Sequentially, one of the unmarked
cells is chosen at random and marked until, aftern steps, each cell is marked. After thekth cell has been marked the configuration of marked cells defines some number of islands: maximal sets of adjacent marked
cells. Let ξ
k
denote the random number of islands afterk cells have been marked.
We give explicit expressions for moments of products of ξ
k
’s and for moments of products of 1/ξ
k
’s.
These are used in a companion paper to prove that if a random graph on the natural number is made by drawing an edge betweeni≧1 andj>i with probabilityλ/j, then the graph is almost surely connected ifλ>1/4 and almost surely disconnected ifλ≦1/4. 相似文献
10.
Linda Kaufmann Hans‐Wolfram Lerner Michael Bolte 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o588-o590
A new polymorph of tetraphenyldiboroxane [or oxybis(diphenylborane)], C24H20B2O, (Ia), has been found. It is monoclinic, like the already known form, (Ib), and can be refined in the same space group, namely P21/c, or in the equivalent setting P21/n. The molecular conformations of the two polymorphs differ in the rotations of two of the phenyl rings about the B—C bonds, leading to markedly different packing patterns and cell dimensions. 相似文献