全文获取类型
收费全文 | 531篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
554篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 23篇 |
2015年 | 27篇 |
2014年 | 31篇 |
2013年 | 27篇 |
2012年 | 48篇 |
2011年 | 46篇 |
2010年 | 24篇 |
2009年 | 29篇 |
2008年 | 38篇 |
2007年 | 34篇 |
2006年 | 24篇 |
2005年 | 27篇 |
2004年 | 22篇 |
2003年 | 21篇 |
2002年 | 16篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有554条查询结果,搜索用时 0 毫秒
41.
42.
The objective of this study was to describe a wide spectrum of surface structural and anatomical details of the Chinese brake
fern (Pteris vittata) using scanning electron microscopy (SEM). SEM revealed that the epidermal cells of the pinnae were elongated with raised
periclinal and sinuous anticlinal walls. The pinnae were hypostomatous with randomly scattered anomocytic stomatal complexes
positioned at the same level as the epidermis. Stomates were large and elliptical (27.4 μm × 10.2 μm). Cross sections from
the central regions of the rachis and the stipe revealed V- and U-shaped vascular bundles, respectively. In each vascular
bundle, the xylem strands were sea-horse shaped (hippocampus). In contrast, the pinnae possessed a triangular vascular bundle
with uniform mesophyll organization comprising of homogenous lobed parenchyma cells. The indumentum consisted of trichomes
and scales, which formed various types of vestiture. Trichomes were borne only on the pinnae and scales on the rachis and
stipe. The roots developed a dense network of long root hairs averaging 244 μm long, and the xylem consisted of tracheids
with scalariform pitting. Sori were submarginal; continuous along both margins of the pinna and were covered with a false
indusium. The sporangia were oblong with a short thick stalk and the annulus was positioned vertically resulting in transverse
dehiscence of the sporangium. The paraphyses were uniseriate, unbranched, septate and found to be intermixed with the sporangia.
The exine of the globose spores was adorned with thick reticulum in which the areoles contained round tubercles. This study
describes surface features in detail, which is essential to studies examining the issue of whether morphological characteristics
are related to arsenic hyperaccumulation inP. vittata. 相似文献
43.
Marian Cristian Stan Richard Klöpsch Aiswarya Bhaskar Jie Li Stefano Passerini Martin Winter 《Liver Transplantation》2013,3(2):231-238
Mechanochemical synthesis of Cu3P in the presence of n‐dodecane results in a material with a secondary particle size distribution of 10 μm, secondary particles which consist of homogeneously agglomerated 20 nm primary particles. The electrochemical performance of Cu3P with lithium is influenced by the reaction depth, in other words by the lower potential cut‐off. During the electrochemical reaction, the displacement of copper by lithium from the Cu3P structure until the formation of Li3P and Cu deteriorates the capacity retention. Improved performance was obtained when the charge potential was limited to 0.50 V (vs. Li/Li+) and the formation of the LixCu3‐xP phase (0 ≤ × ≤ 2). In this case, when the potential is limited to 0.5 V, the capacity is stable for more than 50 cycles. Acceptable electrochemical performances in Li‐ion cells within the voltage range 0.50–2.0 V (vs. Li/Li+) were shown when Cu3P was used as an anode and Li1.2(Ni0.13Mn0.54Co0.13)O2 and LiNi0.5Mn1.5O4 as positive electrode materials. 相似文献
44.
CH Balachiranjeevi Naik S. Bhaskar V. Abhilash S. Akanksha B. C. Viraktamath M. S. Madhav A. S. Hariprasad G. S. Laha M. S. Prasad S. M. Balachandran C. N. Neeraja M. Satendra Kumar P. Senguttuvel K. B. Kemparaju V. P. Bhadana T. Ram G. Harika H. K. Mahadeva Swamy S. K. Hajira A. Yugander K. Pranathi M. Anila G. Rekha M. B. V. N. Kousik T. Dilip Kumar R. K. Swapnil Archana Giri R. M. Sundaram 《Molecular breeding : new strategies in plant improvement》2015,35(7):1-12
45.
Chaparral shrubs in California experience cool, wet winters and hot, dry summers characteristic of mediterranean-type climates; by contrast, morphologically similar close relatives in central Mexico experience summer rainfall. A comparison of closely related species pairs was conducted to examine whether evolutionary divergences in plant hydraulic conductivity were associated with contrasting seasonality of precipitation. Six species pairs in Santa Barbara, California and Tehuacan, Mexico were chosen to test for repeated directional divergences across the habitat contrast. Additionally, evolutionary correlations were examined using phylogenetically independent contrasts (PICs) among a suite of hydraulic traits, including stem- and leaf-specific conductivity, resistance to embolism, wood density, inverse Huber value, and minimum seasonal water potential. Leaf-specific conductivity was generally higher in California, but for most hydraulic traits the species pairs exhibited varied evolutionary trajectories across the climate contrast. A significant correlation was found between divergences in xylem resistance to embolism and minimum seasonal water potential, but no evolutionary trade-off was found between resistance and stem conductivity. Higher leaf-specific conductivity may be adaptive in California, where soil and atmospheric droughts coincide during summer months. This response is consistent with a hydraulic strategy of high leaf water supply under high evaporative demand to prevent excessive drops in water potential. 相似文献
46.
Enterocyte viability and mitochondrial function after graded intestinal ischemia and reperfusion in rats 总被引:6,自引:0,他引:6
Madesh Muniswamy Bhaskar Lakshmi Balasubramanian K.A. 《Molecular and cellular biochemistry》1997,167(1-2):81-87
Ischemia/reperfusion of the small intestine can lead to metabolic and structural alterations in the mucosa. Cellular dysfunction occurs when mitochondrial metabolism is compromised, which may ultimately lead to impaired organ function. The aims of this study were to assess the suppression of cellular and mitochondrial oxidative metabolism and involvement of mitochondria in the ischemia/reperfusion injury. The mitochondria were prepared from isolated enterocytes obtained from the small intestine of anesthetized adult rats following different time periods of ischemia and ischemia followed by 5 min reperfusion. Cellular and mitochondrial function were assessed using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) reduction assay. Ischemia of increasing time periods caused a progressive decrease in cellular and mitochondrial MTT reduction in enterocytes and reperfusion showed further decrease of MTT formazan formation. Inclusion of 1 mM succinate, as respiratory subs trate, showed reversal of suppression of mitochondrial function in 30-60 min ischemia whereas 90 min ischemia or short time period ischemia followed by 5 min reperfusion indicated an irreversible damage to mitochondria. This study indicated that mitochondria are a sensitive target of damage due to oxygen deficiency and possibly due to sudden burst of oxygen free radicals. Mitochondria can withstand short periods of ischemia whereas long duration ischemia or reperfusion results in irreversible damage to mitochondrial function. (Mol Cell Biochem 167: 81-87, 1997) 相似文献
47.
Thangaraj K Chaubey G Kivisild T Selvi Rani D Singh VK Ismail T Carvalho-Silva D Metspalu M Bhaskar LV Reddy AG Chandra S Pande V Prathap Naidu B Adarsh N Verma A Jyothi IA Mallick CB Shrivastava N Devasena R Kumari B Singh AK Dwivedi SK Singh S Rao G Gupta P Sonvane V Kumari K Basha A Bhargavi KR Lalremruata A Gupta AK Kaur G Reddy KK Rao AP Villems R Tyler-Smith C Singh L 《Human heredity》2008,66(1):1-9
We have analyzed 7,137 samples from 125 different caste, tribal and religious groups of India and 99 samples from three populations of Nepal for the length variation in the COII/tRNA(Lys) region of mtDNA. Samples showing length variation were subjected to detailed phylogenetic analysis based on HVS-I and informative coding region sequence variation. The overall frequencies of the 9-bp deletion and insertion variants in South Asia were 1.9 and 0.6%, respectively. We have also defined a novel deep-rooting haplogroup M43 and identified the rare haplogroup H14 in Indian populations carrying the 9-bp deletion by complete mtDNA sequencing. Moreover, we redefined haplogroup M6 and dissected it into two well-defined subclades. The presence of haplogroups F1 and B5a in Uttar Pradesh suggests minor maternal contribution from Southeast Asia to Northern India. The occurrence of haplogroup F1 in the Nepalese sample implies that Nepal might have served as a bridge for the flow of eastern lineages to India. The presence of R6 in the Nepalese, on the other hand, suggests that the gene flow between India and Nepal has been reciprocal. 相似文献
48.
Akif M Masuyer G Schwager SL Bhuyan BJ Mugesh G Isaac RE Sturrock ED Acharya KR 《The FEBS journal》2011,278(19):3644-3650
Human somatic angiotensin I-converting enzyme (ACE), a zinc-dependent dipeptidyl carboxypeptidase, is central to the regulation of the renin-angiotensin aldosterone system. It is a well-known target for combating hypertension and related cardiovascular diseases. In a recent study by Bhuyan and Mugesh [Org. Biomol. Chem. (2011) 9, 1356-1365], it was shown that the selenium analogues of captopril (a well-known clinical inhibitor of ACE) not only inhibit ACE, but also protect against peroxynitrite-mediated nitration of peptides and proteins. Here, we report the crystal structures of human testis ACE (tACE) and a homologue of ACE, known as AnCE, from Drosophila melanogaster in complex with the most promising selenium analogue of captopril (SeCap) determined at 2.4 and 2.35 ? resolution, respectively. The inhibitor binds at the active site of tACE and AnCE in an analogous fashion to that observed for captopril and provide the first examples of a protein-selenolate interaction. These new structures of tACE-SeCap and AnCE-SeCap inhibitor complexes presented here provide important information for further exploration of zinc coordinating selenium-based ACE inhibitor pharmacophores with significant antioxidant activity. 相似文献
49.
50.
Juluru Bhaskar Srinivas Bandari Gouthami Dasari Suresh Paidakula 《Russian Journal of Bioorganic Chemistry》2021,47(4):954-962
Russian Journal of Bioorganic Chemistry - A series of novel hybrids of indole-pyrimidine moieties were synthesized and evaluated for their in vitro anti-cancer, in vitro anti-bacteria and... 相似文献