全文获取类型
收费全文 | 3310篇 |
免费 | 207篇 |
专业分类
3517篇 |
出版年
2023年 | 27篇 |
2022年 | 67篇 |
2021年 | 90篇 |
2020年 | 48篇 |
2019年 | 69篇 |
2018年 | 72篇 |
2017年 | 74篇 |
2016年 | 123篇 |
2015年 | 165篇 |
2014年 | 184篇 |
2013年 | 231篇 |
2012年 | 254篇 |
2011年 | 260篇 |
2010年 | 131篇 |
2009年 | 119篇 |
2008年 | 209篇 |
2007年 | 186篇 |
2006年 | 161篇 |
2005年 | 152篇 |
2004年 | 151篇 |
2003年 | 98篇 |
2002年 | 126篇 |
2001年 | 34篇 |
2000年 | 26篇 |
1999年 | 26篇 |
1998年 | 15篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 51篇 |
1991年 | 31篇 |
1990年 | 19篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1973年 | 6篇 |
1971年 | 5篇 |
1969年 | 9篇 |
排序方式: 共有3517条查询结果,搜索用时 15 毫秒
1.
2.
The advent of social media expands our ability to transmit information and connect with others instantly, which enables us to behave as “social sensors.” Here, we studied concurrent bursty behavior of Twitter users during major sporting events to determine their function as social sensors. We show that the degree of concurrent bursts in tweets (posts) and retweets (re-posts) works as a strong indicator of winning or losing a game. More specifically, our simple tweet analysis of Japanese professional baseball games in 2013 revealed that social sensors can immediately react to positive and negative events through bursts of tweets, but that positive events are more likely to induce a subsequent burst of retweets. We confirm that these findings also hold true for tweets related to Major League Baseball games in 2015. Furthermore, we demonstrate active interactions among social sensors by constructing retweet networks during a baseball game. The resulting networks commonly exhibited user clusters depending on the baseball team, with a scale-free connectedness that is indicative of a substantial difference in user popularity as an information source. While previous studies have mainly focused on bursts of tweets as a simple indicator of a real-world event, the temporal correlation between tweets and retweets implies unique aspects of social sensors, offering new insights into human behavior in a highly connected world. 相似文献
3.
Duygu Findik Qizhong Song Hiroyoshi Hidaka Martin Lavin 《Journal of cellular biochemistry》1995,57(1):12-21
In addition to a role for de novo protein synthesis in apoptosis we have previously shown that activation of a protein phosphatase or loss of activity of a kinase is also important in radiation-induced apoptosis in human cells [Baxter, and Lavin (1992): J Immunol 148:149–1954]. We show here that some inhibitors of protein kinases exacerbate radiation-induced apoptosis in the human cell line BM13674. The specific protein kinase A inhibitor isoquinoline sulfonamide (20 μM) gave rise to significantly increased levels of apoptosis at 2–6 h postirradiation compared to values after radiation exposure only. The same concentration of isoquinolinesulfonamide, which was effective in increasing apoptosis, reduced activity markedly. A 66% inhibition of cyclic AMP-dependent protein kinase A activity occurred in unirradiated cells at this concentration of H89 and activity was reduced to 58% in irradiated cells. Calphostin C, a specific inhibitor of protein kinase C, at a concentration of 0.1 μM, which caused 68% inhibition of enzyme activity in irradiated cells, failed to enhance the level of radiation-induced apoptosis. Other kinase inhibitors did not lead to an additional increase in apoptosis over and above that observed after irradiation. The results obtained here provide further support for an important role for modification of existing proteins during radiation-induced apoptosis. 相似文献
4.
To investigate whether correction of fasting hyperglycemia per se improves the insulin secretion in type 2 diabetic subjects, plasma insulin response to 75 g oral glucose load has been studied after acute and chronic normalization of fasting plasma glucose levels in 7 overt type 2 diabetic subjects. For the acute normalization of elevated fasting plasma glucose levels, an artificial endocrine pancreas was employed. Although fasting plasma glucose concentrations were normalized before the oral glucose challenge, insulin response to oral glucose was not improved compared to those without normalization of fasting plasma glucose levels. After 1-3 month control of hyperglycemia, the insulin response to glucose in the subjects was significantly improved compared to those without treatments. Results indicate that chronic metabolic control is essential for the improvement of insulin response to glucose in type 2 diabetic subjects, and also suggest that the impaired insulin secretion in type 2 diabetes is not due to hyperglycemia per se, but due to the metabolic derangements which lead to chronic hyperglycemia. 相似文献
5.
6.
Identification of a single nucleotide change in a mutant gene for hypoxanthine-guanine phosphoribosyltransferase (HPRTAnn Arbor) 总被引:1,自引:1,他引:0
Shin Fujimori Yuji Hidaka Beverly L. Davidson Thomas D. Palella William N. Kelley 《Human genetics》1988,79(1):39-43
Summary HPRTAnn Arbor is a variant of hypoxanthine (guanine) phosphoribosyl-transferase (HPRT: EC 2.4.2.8), which was identified in two brothers with hyperuricemia and nephrolithiasis. In previous studies, this mutant enzyme was characterized by an increased Km for both substrates, a normal Vmax, a decreased intracellular concentration of enzyme protein, a normal subunit molecular weight and an acidic isoelectric point under native isoelectric focusing conditions. We have cloned a full-length cDNA for HPRTAnn Arbor and determined its complete nucleotide sequence. A single nucleotide change (TG) at nucleotide position 396 has been identified. This transversion predicts an amino acid substitution from isoleucine (ATT) to methionine (ATG) in codon 132, which is located within the putative 5-phosphoribosyl-1-pyrophosphate (PRPP)-binding site of HPRT. 相似文献
7.
Shiraishi Tomonori; Araki Miwa; Yoshioka Hirofumi; Kobayashi Issei; Yamada Tetsuji; Ichinose Yuki; Kunoh Hitoshi; Oku Hachiro 《Plant & cell physiology》1991,32(7):1067-1075
A pathogenic fungus of pea, Mycosphaerella pinodes, secretesa so-called "suppressor" in its pycnospore germination fluid.The suppressor blocks the defense responses and induces localsusceptibility (accessibility) in pea plants to agents thatare not pathogenic in pea. The suppressor nonspecifically inhibitsthe ATPase activity in plasma membranes prepared from pea, soybean,kidney bean, cowpea and barley plants. However, cytochemicalstudies by electron microscopy indicate that the suppressorspecifically inhibits the ATPase in pea cell membranes, butnot in those of four other plant species tested. That is, thespecificity of the suppressor appears at the cell and/or tissuelevel, but is not evident in vitro. Furthermore, the inhibitoryeffect of the suppressor is temporary because the ATPase activityrecovers 9 h after the treatment. A similar effect was observedafter inoculation with M. pinodes but not with a nonpathogenof pea, M. ligulicola. The role of the suppressor in host-parasitespecificity is discussed. (Received April 9, 1991; Accepted August 6, 1991) 相似文献
8.
N Arima Y Daitoku S Hidaka H Tanaka T Katsuki 《Journal of immunology (Baltimore, Md. : 1950)》1985,135(4):2474-2477
A Tac-positive B cell line termed K3B was established from a patient with adult T cell leukemia (ATL). This cell line had EBNA antigen and human T cell leukemic virus (HTLV) provirus besides B1 antigen and surface immunoglobulin. A cloned Tac-positive B cell line termed K3B01 was obtained from K3B by the limiting dilution method. The K3B01 cells were shown to absorb IL 2 activity in a tonsillar IL 2 preparation. By using this cloned cell line and a purified recombinant IL 2 preparation, it was shown that the proliferation of K3B01 cells was enhanced by the addition of recombinant IL 2. Moreover, this response was inhibited by anti-Tac antibody. These results demonstrate definitively that IL 2 acts directly on B cells through IL 2 receptors on them. 相似文献
9.
10.
Mating behaviour ofTokunagayusurika akamusi searching at the resting place (lakeside vegetation, although mating also occurs in the air by swarming) was investigated
at the shore of Lake Biwa. Coinciding with the arrival of newly emerged adults, previously emerged males walked about to search
for mates at the resting place. When a searching male came into contact with a fresh (newly emerged) individual, he attempted
to copulate with it regardless of its sex. Consequently, males copulated with fresh females, which were more likely to be
virgin at the resting place, suggesting that the first male might contribute best to the fertilization. 相似文献