全文获取类型
收费全文 | 6725篇 |
免费 | 580篇 |
国内免费 | 6篇 |
专业分类
7311篇 |
出版年
2023年 | 19篇 |
2022年 | 103篇 |
2021年 | 167篇 |
2020年 | 85篇 |
2019年 | 95篇 |
2018年 | 160篇 |
2017年 | 125篇 |
2016年 | 216篇 |
2015年 | 362篇 |
2014年 | 409篇 |
2013年 | 467篇 |
2012年 | 588篇 |
2011年 | 528篇 |
2010年 | 319篇 |
2009年 | 250篇 |
2008年 | 403篇 |
2007年 | 388篇 |
2006年 | 320篇 |
2005年 | 317篇 |
2004年 | 307篇 |
2003年 | 212篇 |
2002年 | 221篇 |
2001年 | 208篇 |
2000年 | 144篇 |
1999年 | 113篇 |
1998年 | 52篇 |
1997年 | 35篇 |
1996年 | 45篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 39篇 |
1989年 | 34篇 |
1988年 | 31篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 22篇 |
1976年 | 20篇 |
1974年 | 17篇 |
1969年 | 13篇 |
排序方式: 共有7311条查询结果,搜索用时 15 毫秒
121.
A molecular phylogeny of New World emballonurid bats based on parsimony and Bayesian analyses of loci from the three different
nuclear genetic transmission pathways in mammals (autosomal, X, and Y chromosomes) is well supported and independently corroborated by each individual gene tree. This is in contrast to a single
most parsimonious but poorly supported tree based on morphological data, which has only one intergeneric or higher relationship
shared with the molecular phylogeny. Combining the morphological and molecular data partitions results in a tree similar to
the molecular tree suggesting a high degree of homoplasy and low phylogenetic signal in the morphological data set. Behavioral
data are largely incomplete and likewise produce a poorly resolved tree. Nonetheless, patterns of evolution in morphology
and behavior can be investigated by using the molecular tree as a phylogenetic framework. Character optimization of the appearance
of dorsal fur and preferred roosting sites maps consistently and are correlated on the phylogeny. This suggests an association
of camouflage for bats with unusual appearance (two dorsal stripes in Rhynchonycteris and Saccopteryx, or pale fur in Cyttarops and Diclidurus) and roosting in exposed sites (tree trunks or under palm leaves). In contrast, the ancestral states for Old and New World
emballonurids are typically uniform brown or black, and they usually roost in sheltered roosts such as caves and tree hollows.
Emballonuridae is the only family of bats that has a sac-like structure in the wing propatagium, which is found in four New
World genera. Mapping the wing sac character states onto the phylogeny indicates that wing sacs evolved independently within
each genus and that there may be a phylogenetic predisposition for this structure. Ear orientation maps relatively consistently
on the molecular phylogeny and is correlated to echolocation call parameters and foraging behavior, suggesting a phylogenetic
basis for these character systems. 相似文献
122.
Magnesium levels in serum, erythrocytes, skeletal muscle, and bone were measured in 10 patients with valvular heart disease who had received diuretic therapy for heart failure for an average of 3·3 years. Five patients were found to have diminished values for skeletal muscle, indicating significant magnesium deficit. Values for erythrocytes were low in only two of the five patients, and none had low values for serum ultrafiltrate and bone: Magnesium replacement therapy restored skeletal muscle values to normal. Clinical features consistent with the presence of magnesium deficiency were found in all five magnesium-deficient patients. These features were, with few exceptions, corrected by magnesium replacement. The latter also corrected low skeletal muscle potassium values present in all five patients with low skeletal muscle magnesium, four of whom showed clinical features of digoxin poisoning before magnesium therapy was given. Concomitant secondary aldosteronism, inadequate dietary intake, and digoxin therapy had probably augmented the magnesium loss due to diuretic therapy. 相似文献
123.
Protein arginine methyltransferase 5 (PRMT5) is a major enzyme responsible for generating monomethyl and symmetric dimethyl arginine in proteins. PRMT5 is essential for cell viability and development, and its overexpression is observed in a variety of cancers. In the present study, it is found that levels of PRMT5 protein and symmetric arginine dimethylation in colorectal cancer (CRC) tissues are increased compared to those in adjacent noncancerous tissues. Using immunoaffinity enrichment of methylated peptides combined with high‐resolution mass spectrometry, a total of 147 symmetric dimethyl‐arginine (SDMA) sites in 94 proteins are identified, many of which are RNA binding proteins and enzymes. Quantitative analysis comparing CRC and normal tissues reveals significant increase in the symmetric dimethylation of 70 arginine sites in 46 proteins and a decrease in that of four arginine sites in four proteins. Among the 94 proteins identified in this study, it is confirmed that KH‐type splicing regulatory protein is a target of PRMT5 and highly expressed in CRC tissues compared to noncancerous tissues. This study is the first comprehensive analysis of symmetric arginine dimethylation using clinical samples and extends the number of known in vivo SDMA sites. The data obtained are available via ProteomeXchange with the identifier PXD015653. 相似文献
124.
125.
Rahman Daiyan Emma Catherine Lovell Bosi Huang Muhammad Zubair Joshua Leverett Qingran Zhang Sean Lim Jonathan Horlyck Jianbo Tang Xunyu Lu Kourosh Kalantar‐Zadeh Judy N. Hart Nicholas M. Bedford Rose Amal 《Liver Transplantation》2020,10(28)
In this study, scalable, flame spray synthesis is utilized to develop defective ZnO nanomaterials for the concurrent generation of H2 and CO during electrochemical CO2 reduction reactions (CO2RR). The designed ZnO achieves an H2/CO ratio of ≈1 with a large current density (j) of 40 mA cm?2 during long‐term continuous reaction at a cell voltage of 2.6 V. Through in situ atomic pair distribution function analysis, the remarkable stability of these ZnO structures is explored, addressing the knowledge gap in understanding the dynamics of oxide catalysts during CO2RR. Through optimization of synthesis conditions, ZnO facets are modulated which are shown to affect reaction selectivity, in agreement with theoretical calculations. These findings and insights on synthetic manipulation of active sites in defective metal‐oxides can be used as guidelines to develop active catalysts for syngas production for renewable power‐to‐X to generate a range of fuels and chemicals. 相似文献
126.
Richard W. Clayton Ewan A. Langan David M. Ansell Ivo J. H. M. de Vos Klaus Gbel Marlon R. Schneider Mauro Picardo Xinhong Lim Maurice A. M. van Steensel Ralf Paus 《Biological reviews of the Cambridge Philosophical Society》2020,95(3):592-624
The nervous system communicates with peripheral tissues through nerve fibres and the systemic release of hypothalamic and pituitary neurohormones. Communication between the nervous system and the largest human organ, skin, has traditionally received little attention. In particular, the neuro‐regulation of sebaceous glands (SGs), a major skin appendage, is rarely considered. Yet, it is clear that the SG is under stringent pituitary control, and forms a fascinating, clinically relevant peripheral target organ in which to study the neuroendocrine and neural regulation of epithelia. Sebum, the major secretory product of the SG, is composed of a complex mixture of lipids resulting from the holocrine secretion of specialised epithelial cells (sebocytes). It is indicative of a role of the neuroendocrine system in SG function that excess circulating levels of growth hormone, thyroxine or prolactin result in increased sebum production (seborrhoea). Conversely, growth hormone deficiency, hypothyroidism, and adrenal insufficiency result in reduced sebum production and dry skin. Furthermore, the androgen sensitivity of SGs appears to be under neuroendocrine control, as hypophysectomy (removal of the pituitary) renders SGs largely insensitive to stimulation by testosterone, which is crucial for maintaining SG homeostasis. However, several neurohormones, such as adrenocorticotropic hormone and α‐melanocyte‐stimulating hormone, can stimulate sebum production independently of either the testes or the adrenal glands, further underscoring the importance of neuroendocrine control in SG biology. Moreover, sebocytes synthesise several neurohormones and express their receptors, suggestive of the presence of neuro‐autocrine mechanisms of sebocyte modulation. Aside from the neuroendocrine system, it is conceivable that secretion of neuropeptides and neurotransmitters from cutaneous nerve endings may also act on sebocytes or their progenitors, given that the skin is richly innervated. However, to date, the neural controls of SG development and function remain poorly investigated and incompletely understood. Botulinum toxin‐mediated or facial paresis‐associated reduction of human sebum secretion suggests that cutaneous nerve‐derived substances modulate lipid and inflammatory cytokine synthesis by sebocytes, possibly implicating the nervous system in acne pathogenesis. Additionally, evidence suggests that cutaneous denervation in mice alters the expression of key regulators of SG homeostasis. In this review, we examine the current evidence regarding neuroendocrine and neurobiological regulation of human SG function in physiology and pathology. We further call attention to this line of research as an instructive model for probing and therapeutically manipulating the mechanistic links between the nervous system and mammalian skin. 相似文献
127.
128.
Youngkyoung Lim Hyun‐Tae Shin YoungHwan Choi Dong‐Youn Lee 《Pigment cell & melanoma research》2020,33(2):318-325
Melanoma can develop in a congenital melanocytic nevus (CMN). In fact, a large CMN is associated with a high risk of developing melanoma. Although melanomas arising from CMNs are thought to have a pathogenesis distinct from conventional melanomas, no studies have been conducted on the evolution or tumor heterogeneity of CMN melanomas. We applied multi‐region whole‐exome sequencing to investigate the clonal nature of driver events and evolutionary processes in CMNs and melanomas arising from CMNs. In two patients, we observed an independent subclonal evolution in cancerized fields of CMNs and chromosome 8q amplification in both melanomas arising from CMNs. The amplification of MYC, located in chromosome 8q, was correlated with the percentage of tumor cells expressing high levels of MYC protein detected in melanoma cells by immunohistochemistry. Our analysis suggests that each CMN cell may evolve sporadically and that amplification of MYC might be a key event for melanoma development in CMNs. 相似文献
129.
Jinho Yoon Minkyu Shin Joungpyo Lim Dong Yeon Kim Taek Lee Jeong‐Woo Choi 《Biotechnology journal》2020,15(6)
Biomolecules, especially proteins and nucleic acids, have been widely studied to develop biochips for various applications in scientific fields ranging from bioelectronics to stem cell research. However, restrictions exist due to the inherent characteristics of biomolecules, such as instability and the constraint of granting the functionality to the biochip. Introduction of functional nanomaterials, recently being researched and developed, to biomolecules have been widely researched to develop the nanobiohybrid materials because such materials have the potential to enhance and extend the function of biomolecules on a biochip. The potential for applying nanobiohybrid materials is especially high in the field of bioelectronics. Research in bioelectronics is aimed at realizing electronic functions using the inherent properties of biomolecules. To achieve this, various biomolecules possessing unique properties have been combined with novel nanomaterials to develop bioelectronic devices such as highly sensitive electrochemical‐based bioelectronic sensing platforms, logic gates, and biocomputing systems. In this review, recently reported bioelectronic devices based on nanobiohybrid materials are discussed. The authors believe that this review will suggest innovative and creative directions to develop the next generation of multifunctional bioelectronic devices. 相似文献
130.
In-Soo Lim 《Journal of Exercise Nutrition & Biochemistry》2020,24(4):28
[Purpose] This study aimed to investigate the effects of branched-chain amino acid (BCAA) supplement on delayed onset muscle soreness (DOMS) by analyzing the maximum muscle strength and indicators of muscle damage.[Methods] Twelve men with majors in physical education were assigned to the BCAA group and placebo group in a double-blinded design, and repeated measurements were conducted. DOMS was induced with an isokinetic exercise. Following BCAA administration, the changes in the knee extension peak torque, flexion peak torque, aspartate aminotransferase (AST), creatine kinase (CK), and lactate dehydrogenase (LDH) concentrations were analyzed. The maximum knee muscle strength was measured at the baseline (pre-D0) following BCAA administration for 5 days before exercise (-D5, -4D, -3D, -2D, -1D). In contrast, the post-treatment measurements (D3) were recorded after BCAA administration for 3 days (post-D0, D1, D2). Blood samples were obtained before (pre-D0), immediately after (post-D0), 24 h (D1), 48 h (D2), and 72 h (D3) after the exercise to analyze the indicators of muscle strength. BCAA was administered twice daily for 8 days (5 days and 3 days before inducing DOMS and during the experimental period, respectively).[Results] There was no difference in the flexion peak torque between the groups. However, the BCAA group showed a significantly higher extension peak torque at D3 (second isokinetic exercise), compared to the placebo group (p<.05). There was no difference in AST changes between the groups. Nonetheless, the CK and LDH were significantly reduced in the BCAA group, compared to the placebo group. There was no correlation between the extension peak torque and flexion peak torque. However, the CK and LDH increased proportionately in DOMS. Moreover, their concentrations significantly increased with a decreasing peak torque (p<.01).[Conclusion] An exercise-induced DOMS results in a decrease in the peak torque and a proportional increase in the CK and LDH concentrations. Moreover, the administration of BCAA inhibits the reduction of the extension peak torque and elevation of CK and LDH concentrations. Therefore, BCAA might be administered as a supplement to maintain the muscle strength and prevent muscle damage during vigorous exercises that may induce DOMS in sports settings. 相似文献