全文获取类型
收费全文 | 531篇 |
免费 | 32篇 |
出版年
2022年 | 10篇 |
2021年 | 19篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 23篇 |
2014年 | 28篇 |
2013年 | 43篇 |
2012年 | 40篇 |
2011年 | 39篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 32篇 |
2007年 | 29篇 |
2006年 | 31篇 |
2005年 | 25篇 |
2004年 | 20篇 |
2003年 | 19篇 |
2002年 | 19篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有563条查询结果,搜索用时 15 毫秒
501.
In an effort to determine the chemical diversity of the Valeriana genera of the Northwestern Himalaya (Uttaranchal), V. wallichii, V. himalayana (syn. V. dioica), V. pyrolaefolia, and V. hardwickii var. arnottiana were investigated for their terpenoid compositions by means of GC and GC/MS analyses of their essential oils, as well as by one- and two-dimensional NMR studies of the isolates. Our results establish that V. wallichii DC. includes two stable chemotypes, with no mixed population, chemotype I being characterized by the presence of maaliol (1), and chemotype II having patchouli alcohol (2) and 8-acetoxypatchouli alcohol (3) as major compounds. V. hardwickii var. arnottiana was also found to exist as two independent chemotypes. Here, chemotype I is characterized by alpha-kessyl acetate (4), valeracetate (5), and 8-epikessyl glycol diacetate (6), whereas the chemotype-II species contain maaliol (1) and kessanyl acetate (7). V. himalayana Grub. had maaliol (1), valeranone (8), kessane (9), and alpha-kessyl acetate (4) as major compounds, and V. pyrolaefolia Decne. contained patchouli alcohol (2) and valeranone (8) as markers. 相似文献
502.
Orer HS Gebber GL Phillips SW Barman SM 《American journal of physiology. Regulatory, integrative and comparative physiology》2004,286(3):R451-R464
We tested the hypothesis that blockade of N-methyl-D-aspartate (NMDA) and non-NMDA receptors on medullary lateral tegmental field (LTF) neurons would reduce the sympathoexcitatory responses elicited by electrical stimulation of vagal, trigeminal, and sciatic afferents, posterior hypothalamus, and midbrain periaqueductal gray as well as by activation of arterial chemoreceptors with intravenous NaCN. Bilateral microinjection of a non-NMDA receptor antagonist into LTF of urethane-anesthetized cats significantly decreased vagal afferent-evoked excitatory responses in inferior cardiac and vertebral nerves to 29 +/- 8 and 24 +/- 6% of control (n = 7), respectively. Likewise, blockade of non-NMDA receptors significantly reduced chemoreceptor reflex-induced increases in inferior cardiac (from 210 +/- 22 to 129 +/- 13% of control; n = 4) and vertebral nerves (from 253 +/- 41 to 154 +/- 20% of control; n = 7) and mean arterial pressure (from 39 +/- 7 to 21 +/- 5 mmHg; n = 8). Microinjection of muscimol, but not an NMDA receptor antagonist, caused similar attenuation of these excitatory responses. Sympathoexcitatory responses to the other stimuli were not attenuated by microinjection of a non-NMDA receptor antagonist or muscimol into LTF. In fact, excitatory responses elicited by stimulation of trigeminal, and in some cases sciatic, afferents were enhanced. These data reveal two new roles for the LTF in control of sympathetic nerve activity in cats. One, LTF neurons are involved in mediating sympathoexcitation elicited by activation of vagal afferents and arterial chemoreceptors, primarily via activation of non-NMDA receptors. Two, non-NMDA receptor-mediated activation of other LTF neurons tonically suppresses transmission in trigeminal-sympathetic and sciatic-sympathetic reflex pathways. 相似文献
503.
Trioxanes 8a-b, easily accessible in two steps from allylic alcohol 6a-b, on reductive amination with 4-aminoquinolines 4a-c furnish a new series of trioxaquines 9a-b, 10a-b, 11a-b in 32-77% yields. Dicitrate salts of these trioxaquines have been evaluated for antimalarial activity against multidrug resistant Plasmodium yoelii in mice model. 相似文献
504.
Sympathetic nerve and cardiovascular responses to chemical activation of the midbrain defense region
Larsen PD Zhong S Gebber GL Barman SM 《American journal of physiology. Regulatory, integrative and comparative physiology》2001,280(6):R1704-R1712
The changes in mean arterial pressure (MAP), renal (RBF) and femoral (FBF) blood flows, and inferior cardiac (CN) and vertebral nerve (VN) sympathetic nerve discharges (SND) produced by chemical activation (D,L-homocysteic acid) of the midbrain periaqueductal gray (PAG) were compared in baroreceptor-denervated and -innervated cats anesthetized with urethan. Defenselike cardiovascular responses in both states were similar in magnitude and consisted of increased MAP and FBF and decreased RBF; however, the nerve responses differed. In baroreceptor-denervated cats, PAG activation increased CN 10-Hz activity, decreased VN 10-Hz activity, and lengthened the CN-VN phase angle. In baroreceptor-innervated cats in which the rhythm in SND was cardiac related, PAG activation increased CN activity, but VN activity and the CN-VN phase angle were unchanged. These results demonstrate that chemical activation of PAG neurons induces differential patterns of sympathetic outflow generally consistent with accompanying defenselike cardiovascular responses. However, the mechanisms responsible for the changes in 10-Hz and cardiac-related SND appear to be different. 相似文献
505.
Like virtually all other physiological control systems, the sympathetic nervous system controlling cardiovascular function is characterized by the presence of rhythmic activity. These include slow rhythms with frequencies at or below that of the respiration and rapid rhythms with frequencies at or above that of the heart beat. The rapid rhythms are the subject of this review. The specific questions entertained are as follows: (1) Are the rapid cardiac-related and 10-Hz rhythms inherent to central sympathetic networks, or are they imposed on sympathetic nerve discharge (SND) by extrinsic periodic inputs? (2) Does basal SND arise from an anatomically circumscribed "vasomotor center" composed of pacemaker neurons in the rostral ventrolateral medulla or from an anatomically distributed network oscillator composed of different types of brainstem neurons, none of which necessarily have intrinsic pacemaker properties? (3) Are the rapid rhythms generated by single circuits or by systems of coupled oscillators, each with a separate target? (4) Are the rapid rhythms in SND simply by-products of the sympathetic generating mechanisms, or do they subserve selective and special functions, such as the formulation of differential patterns of spinal sympathetic outflow that support particular behaviors? The controversial aspects of these issues and the state-of-the-art analytical methods used to study them are stressed in this review. 相似文献
506.
Chandan Shrestha Takashi Ito Ko-ichi Kawahara Binita Shrestha Munekazu Yamakuchi Teruto Hashiguchi Ikuro Maruyama 《Biochemical and biophysical research communications》2013
Chronic low-grade inflammation is a key contributor to high-fat diet (HFD)-related diseases, such as type 2 diabetes, non-alcoholic steatohepatitis, and atherosclerosis. The inflammation is characterized by infiltration of inflammatory cells, particularly macrophages, into obese adipose tissue. However, the molecular mechanisms by which a HFD induces low-grade inflammation are poorly understood. Here, we show that histone H3, a major protein component of chromatin, is released into the extracellular space when mice are fed a HFD or macrophages are stimulated with the saturated fatty acid palmitate. In a murine macrophage cell line, RAW 264.7, palmitate activated reactive oxygen species (ROS) production and JNK signaling. Inhibitors of these pathways dampened palmitate-induced histone H3 release, suggesting that the extracellular release of histone H3 was mediated, in part, through ROS and JNK signaling. Extracellular histone activated endothelial cells toexpress the adhesion molecules ICAM-1 and VCAM-1 and the procoagulant molecule tissue factor, which are known to contribute to inflammatory cell recruitment and thrombosis. These results suggest the possible contribution of extracellular histone to the pathogenesis of HFD-induced inflammation and thrombosis. 相似文献
507.
508.
Isolation of active fraction and characterization of chemosignals from urine have been attempted in several mammalian species in the recent years. The objective of this study was to identify the urinary volatiles across various reproductive stages of buffalo cow, namely, estrus, diestrus, and pregnancy, and in bull, by chemical extraction followed by gas chromatography–linked mass spectrometry (GC-MS). Urine samples were collected from six buffalo cows at two different phases of estrous cycle, namely, estrus and diestrus. Besides, urinary samples were collected from five pregnant buffalo cows (60–75 days after artificial insemination (AI)) and six adult bulls. Thin-layer chromatography was performed as a preliminary test for qualitative comparison of different compounds extracted by organic solvents. Identification of the urinary compounds was carried out in a gas chromatograph (Perkin Elmer, Autosystem XL) linked to a mass spectrometer (Turbomass). The results of GC-MS analysis indicated the presence of 21 compounds with varying molecular weights and retention time, which were further categorized as diestrus-specific, pregnancy-specific, and bull-specific urinary compounds. No compound, however, could be identified as estrus-specific. We concluded that qualitative differences do exist in estrus, diestrus, and pregnant buffalo cow urine and in bull urine, as evidenced by GC-MS. 相似文献
509.
Irfan A. Asangani Bushra Ateeq Qi Cao Lois Dodson Mithil Pandhi Lakshmi P. Kunju Rohit Mehra Robert J. Lonigro Javed Siddiqui Nallasivam Palanisamy Yi-Mi Wu Xuhong Cao Jung H. Kim Meng Zhao Zhaohui S. Qin Mathew K. Iyer Christopher A. Maher Chandan Kumar-Sinha Arul M. Chinnaiyan 《Molecular cell》2013,49(1):80-93
510.
Ratan Kumar Rai Afzal Azim Neeraj Sinha Jyoti Narayan Sahoo Chandan Singh Armin Ahmed Saurabh Saigal Arvind Kumar Baronia Devendra Gupta Mohan Gurjar Banani Poddar Ratendra Kumar Singh 《Metabolomics : Official journal of the Metabolomic Society》2013,9(3):667-676
We present a method for identifying biomarkers in human lung injury. The method is based on high-resolution nuclear magnetic resonance (NMR) spectroscopy applied to bronchoalveolar lavage fluid (BALF) collected from lungs of critically ill patients. This biological fluid can be obtained by bronchoscopic and non-bronchoscopic methods. The type of lung injury in acute respiratory failure presenting as acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), continues to challenge critical care physicians. We characterize different metabolites in BAL fluid by non-bronchoscopic method (mBALF) for better diagnosis and understanding of ALI/ARDS by NMR spectroscopy. NMR spectra of mBALF collected from 30 patients (9 controls, 10 ARDS and 11 ALI) were analyzed for the identification of biomarkers. Statistical methods such as principal components analysis and partial least square discriminant analysis were carried out on 1H NMR spectrum of mBALF to identify biomarker responsible for separation among different lung injuries classes (ALI and ARDS) and normal lungs. The corresponding correlation of biomarkers with metabolic cycle has given insight into metabolism of lung injuries in critically ill patients. Our study shows statistically significant differentiation of various metabolites concentration in mBALF collected from lungs of ALI, ARDS and healthy control patients, making NMR spectroscopy as a possible new method of characterizing human lung injury. 相似文献