全文获取类型
收费全文 | 174篇 |
免费 | 5篇 |
专业分类
化学 | 117篇 |
晶体学 | 15篇 |
力学 | 9篇 |
数学 | 3篇 |
物理学 | 35篇 |
出版年
2023年 | 2篇 |
2018年 | 1篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 5篇 |
2007年 | 9篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1942年 | 1篇 |
1936年 | 2篇 |
1928年 | 1篇 |
1896年 | 2篇 |
排序方式: 共有179条查询结果,搜索用时 281 毫秒
101.
102.
103.
The "resident" ecotype of killer whales (Orcinus orca) in the waters of British Columbia and Washington State have a strong preference for Chinook salmon even in months when Chinook comprise less than about 10% of the salmon population. The foraging behavior of killer whales suggests that they depend on echolocation to detect and recognize their prey. In order to determine possible cues in echoes from salmon species, a series of backscatter measurements were made at the Applied Physics Laboratory (Univ. of Wash.) Facility on Lake Union, on three different salmon species using simulated killer whale echolocation signals. The fish were attached to a monofilament net panel and rotated while echoes were collected, digitized and stored on a laptop computer. Three transducer depths were used; same depth, 22° and 45° above the horizontal plane of the fish. Echoes were collected from five Chinook, three coho and one sockeye salmon. Radiograph images of all specimens were obtained to examine the swimbladder shape and orientation. The results show that echo structure from similar length but different species of salmon were different and probably recognizable by foraging killer whales. 相似文献
104.
Michael Horne 《Foundations of Physics》2012,42(1):140-146
A generic non-conservative force, applied to an interferometer particle for a period in the past and then turned off, leaves
stationary phase and fringe shifts in the now force-free interferometer. Both Aharonov-Bohm and Aharonov-Casher topological
phase and fringe shifts can be created in this way. The specific sources of the non-conservative forces behind Aharonov-Bohm
and Aharonov-Casher stationary fringe shifts are, respectively, Faraday induction fields and Maxwell displacement currents,
now off. 相似文献
105.
Sexton M Woodruff G Horne EA Lin YH Muccioli GG Bai M Stern E Bornhop DJ Stella N 《Chemistry & biology》2011,18(5):563-568
High-throughput screening (HTS) of chemical libraries is often used for the unbiased identification of compounds interacting with G protein-coupled receptors (GPCRs), the largest family of therapeutic targets. However, current HTS methods require removing GPCRs from their native environment, which modifies their pharmacodynamic properties and biases the screen toward false positive hits. Here, we developed and validated a molecular imaging (MI) agent, NIR-mbc94, which emits near infrared (NIR) light and selectively binds to endogenously expressed cannabinoid CB(2) receptors,?a recognized target for treating autoimmune diseases, chronic pain and cancer. The precision and ease of this assay allows for the HTS of compounds interacting with CB(2) receptors expressed in their native environment. 相似文献
106.
Chi Y English EP Pomerantz WC Horne WS Joyce LA Alexander LR Fleming WS Hopkins EA Gellman SH 《Journal of the American Chemical Society》2007,129(18):6050-6055
Proline-catalyzed diastereoselective aminomethylation of aldehydes using a chiral iminium ion, generated from a readily prepared precursor, provides alpha-substituted-beta-amino aldehydes with 85:15 to 90:10 dr. The alpha-substituted-beta-amino aldehydes can be reduced to beta-substituted-gamma-amino alcohols, the major diastereomer of which can be isolated via crystallization or column chromatography. The amino alcohols are efficiently transformed to protected beta2-amino acids, which are valuable building blocks for beta-peptides, natural products, and other interesting molecules. Because conditions for the aminomethylation and subsequent reactions are mild, beta2-amino acid derivatives with protected functional groups in the side chain, such as beta2-homoglutamic acid, beta2-homotyrosine, and beta2-homolysine, can be prepared in this way. The synthetic route is short, and purifications are simple; therefore, this method enables the preparation of protected beta2-amino acids in useful quantities. 相似文献
107.
108.
The first total synthesis of (+)-frondosin A was accomplished in 19 longest linear and 21 total steps from commercially available materials. The key features of the synthesis include a Ru-catalyzed [5+2] cycloaddition, a Claisen rearrangement, and a ring expansion to construct the core of the frondosin A in a diastereoselective and regioselective fashion. This is the first application of a Ru-catalyzed [5+2] cycloaddition in the total synthesis of a natural product. Through this synthesis, the absolute configuration of (+)-frondosin A was established. 相似文献
109.
Flow characteristics in the vicinity of the flap of a single-slotted airfoil are presented and analysed. The flow remained attached over the model surfaces except in the vicinity of the flap trailing edge where a small region of boundary-layer separation extended over the aft 7% of flap chord. The airfoil configuration was tested at a Mach number of 0.09 and a chord Reynolds number of 1.8 × 106 in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The flow was complicated by the presence of a strong, initially inviscid, jet, emanating from the slot between airfoil and flap, and a gradual merging of the main airfoil wake and flap suction-side boundary layer.Research Engineer, NRC Research AssociateAerospace Engineer 相似文献
110.
The Double‐Histidine Cu2+‐Binding Motif: A Highly Rigid,Site‐Specific Spin Probe for Electron Spin Resonance Distance Measurements 下载免费PDF全文
Timothy F. Cunningham Miriam R. Putterman Astha Desai Prof. W. Seth Horne Prof. Sunil Saxena 《Angewandte Chemie (International ed. in English)》2015,54(21):6330-6334
The development of ESR methods that measure long‐range distance distributions has advanced biophysical research. However, the spin labels commonly employed are highly flexible, which leads to ambiguity in relating ESR measurements to protein‐backbone structure. Herein we present the double‐histidine (dHis) Cu2+‐binding motif as a rigid spin probe for double electron–electron resonance (DEER) distance measurements. The spin label is assembled in situ from natural amino acid residues and a metal salt, requires no postexpression synthetic modification, and provides distance distributions that are dramatically narrower than those found with the commonly used protein spin label. Simple molecular modeling based on an X‐ray crystal structure of an unlabeled protein led to a predicted most probable distance within 0.5 Å of the experimental value. Cu2+ DEER with the dHis motif shows great promise for the resolution of precise, unambiguous distance constraints that relate directly to protein‐backbone structure and flexibility. 相似文献