全文获取类型
收费全文 | 9183篇 |
免费 | 561篇 |
国内免费 | 2篇 |
出版年
2023年 | 20篇 |
2022年 | 47篇 |
2021年 | 116篇 |
2020年 | 75篇 |
2019年 | 83篇 |
2018年 | 140篇 |
2017年 | 107篇 |
2016年 | 194篇 |
2015年 | 275篇 |
2014年 | 348篇 |
2013年 | 575篇 |
2012年 | 546篇 |
2011年 | 539篇 |
2010年 | 353篇 |
2009年 | 350篇 |
2008年 | 606篇 |
2007年 | 569篇 |
2006年 | 581篇 |
2005年 | 562篇 |
2004年 | 575篇 |
2003年 | 508篇 |
2002年 | 456篇 |
2001年 | 184篇 |
2000年 | 168篇 |
1999年 | 140篇 |
1998年 | 118篇 |
1997年 | 99篇 |
1996年 | 65篇 |
1995年 | 77篇 |
1994年 | 67篇 |
1993年 | 66篇 |
1992年 | 105篇 |
1991年 | 88篇 |
1990年 | 78篇 |
1989年 | 84篇 |
1988年 | 86篇 |
1987年 | 71篇 |
1986年 | 70篇 |
1985年 | 50篇 |
1984年 | 56篇 |
1983年 | 45篇 |
1982年 | 46篇 |
1981年 | 41篇 |
1980年 | 35篇 |
1979年 | 50篇 |
1978年 | 31篇 |
1977年 | 32篇 |
1976年 | 24篇 |
1974年 | 25篇 |
1973年 | 22篇 |
排序方式: 共有9746条查询结果,搜索用时 0 毫秒
1.
2.
Julie A. Harris Akihiko Koyama Sumihiro Maeda Kaitlyn Ho Nino Devidze Dena B. Dubal Gui-Qiu Yu Eliezer Masliah Lennart Mucke 《PloS one》2012,7(9)
Accumulation of hyperphosphorylated tau in the entorhinal cortex (EC) is one of the earliest pathological hallmarks in patients with Alzheimer’s disease (AD). It can occur before significant Aβ deposition and appears to “spread” into anatomically connected brain regions. To determine whether this early-stage pathology is sufficient to cause disease progression and cognitive decline in experimental models, we overexpressed mutant human tau (hTauP301L) predominantly in layer II/III neurons of the mouse EC. Cognitive functions remained normal in mice at 4, 8, 12 and 16 months of age, despite early and extensive tau accumulation in the EC. Perforant path (PP) axon terminals within the dentate gyrus (DG) contained abnormal conformations of tau even in young EC-hTau mice, and phosphorylated tau increased with age in both the EC and PP. In old mice, ultrastructural alterations in presynaptic terminals were observed at PP-to-granule cell synapses. Phosphorylated tau was more abundant in presynaptic than postsynaptic elements. Human and pathological tau was also detected within hippocampal neurons of this mouse model. Thus, hTauP301L accumulation predominantly in the EC and related presynaptic pathology in hippocampal circuits was not sufficient to cause robust cognitive deficits within the age range analyzed here. 相似文献
3.
4.
Ishida Takuya Uehara Yoshitoshi Ikeya Tohru Haraguchi Takashi F. Asano Satoshi Ogino Yohei Okuda Noboru 《Limnology》2020,21(3):403-413
Limnology - Controlling phosphorous (P) loads from rice fields is important for the conservation of aquatic ecosystems, in part because P is relatively concentrated at its sources. Recently, winter... 相似文献
5.
In order to control visually-guided voluntary movements, the central nervous system (CNS) must solve the following three computational problems at different levels: (1) determination of a desired trajectory in the visual coordinates, (2) transformation of the coordinates of the desired trajectory to the body coordinates and (3) generation of motor command. In this paper, the second and the third problems are treated at computational, representational and hardware levels of Marr. We first study the problems at the computational level, and then propose an iterative learning scheme as a possible algorithm. This is a trial and error type learning such as repetitive training of golf swing. The amount of motor command needed to coordinate activities of many muscles is not determined at once, but in a step-wise, trial and error fashion in the course of a set of repetitions. Actually, the motor command in the (n+1)-th iteration is a sum of the motor command in then-th iteration plus two modification terms which are, respectively, proportional to acceleration and speed errors between the desired trajectory and the realized trajectory in then-th iteration. We mathematically formulate this iterative learning control as a Newton-like method in functional spaces and prove its convergence under appropriate mathematical conditions with use of dynamical system theory and functional analysis. Computer simulations of this iterative learning control of a robotic manipulator in the body or visual coordinates are shown. Finally, we propose that areas 2, 5, and 7 of the sensory association cortex are possible sites of this learning control. Further we propose neural network model which acquires transformation matrices from acceleration or velocity to motor command, which are used in these schemes. 相似文献
6.
Satoshi Shizukuishi Satoshi Nishii John Ellis Karl Folkers 《Biochemical and biophysical research communications》1980,95(3):1126-1130
The mean basal specific activities and the mean % deficiencies of the activity of the glutamic oxaloacetic transaminase of the erythrocytes were identical (n.s.) for a group of eight patients with a severe carpal tunnel syndrome and for a group of eight university students. There was no significant difference in the increases in the specific activities for the patients and the students at 4 concentrations of pyridoxal 5′-phosphate. The apparent Km for the patients and the students was 95 μM and 61 μM (n.s.) respectively. It is concluded from these data in conjunction with previous findings that the carpal tunnel syndrome is a deficiency disease of vitamin B6, which is probably primary rather than one of a dependency state. 相似文献
7.
8.
Two species of fiddler crab, Uca tetragonon(Herbst, 1790) and Uca vocans(Linnaeus, 1758), which belong to the subgenus Gelasimus, dwell on rocky shores and muddy–sandy tidal flats, respectively, in Phuket Is., Thailand. We investigated their feeding ecology in relation to the morphology of their feeding organs: minor food-handling chelipeds and maxillipeds. U. tetragononfed chiefly on rocks covered by filamentous green algae. U. vocansfed on the emerged sand and in shallow water along the shoreline and in pools. While feeding, both crabs made sand pellets beneath their mouthparts and discarded them, indicating that they divided the matter scooped up with their minor chelipeds into edible and inedible fractions by using the maxillipeds in the water passing through their buccal cavity. The morphology of maxillipeds hardly differed between the two species, which means that both species are flotation-feeders. The morphology of their minor chelipeds, however, differed: the tips of the dactyl and pollex were flat in U. tetragononand pointed in U. vocans.When the minor cheliped was closed, U. tetragononhad a hemispherical space in the distal one-fourth of the gape, which was closed by the framing keratin layers and a few setae of the dactyl and pollex. On the other hand, U. vocanshad an ellipsoidal space in the distal half of the gape. We consider these morphological characters to be adaptations to the different feeding substrates for retaining more food-laden sediment. We discuss the role of the setae on the minor chelipeds on the basis of the morphological differences between populations of U. tetragononin Phuket Is. and East Africa where the crab inhabits muddy–sandy tidal flats. 相似文献
9.
Junko Maeda Charles R. Yurkon Yoshihiro Fujii Hiroshi Fujisawa Sayaka Kato Colleen A. Brents Mitsuru Uesaka Akira Fujimori Hisashi Kitamura Takamitsu A. Kato 《PloS one》2015,10(12)
When energetic particles irradiate matter, it becomes activated by nuclear reactions. Radioactivation induced cellular effects are not clearly understood, but it could be a part of bystander effects. This investigation is aimed at understanding the biological effects from radioactivation in solution induced by hadron radiation. Water or phosphate buffered saline was activated by being exposed to hadron radiation including protons, carbon- and iron-ions. 1 mL of radioactivated solution was transferred to flasks with Chinese hamster ovary (CHO) cells cultured in 5 mL of complete media. The induction of sister chromatid exchanges (SCE) was used to observe any increase in DNA damage responses. The energy spectrum and the half-lives of the radioactivation were analyzed by NaI scintillation detector in order to identify generated radionuclides. In the radioactivated solution, 511 keV gamma-rays were observed, and their half-lives were approximately 2 min, 10 min, and 20 min. They respectively correspond to the beta+ decay of 15O, 13N, and 11C. The SCE frequencies in CHO cells increased depending on the amount of radioactivation in the solution. These were suppressed with a 2-hour delayed solution transfer or pretreatment with dimethyl sulfoxide (DMSO). Our results suggest that the SCE induction by radioactivated solution was mediated by free radicals produced by the annihilated gamma-rays. Since the SCE induction and DMSO modulation are also reported in radiation-induced bystander effects, our results imply that radioactivation of the solution may have some contribution to the bystander effects from hadron radiation. Further investigations are required to assess if radioactivation effects would attribute an additional level of cancer risk of the hadron radiation therapy itself. 相似文献
10.
Eiji Niwa En-Sheng Chen Satoshi Kanoh Teruo Nakayama 《Bioscience, biotechnology, and biochemistry》2013,77(11):3067-3071
The linearity of the stress-strain relationship for food gel is limited to a very narrow range of the strain (usually less than 0.1 as a Cauchy measure). The reason is thought due to the change in cross-sectional area of the gel upon deformation. In this report, the cross-sectional area was approximately corrected of the compressed gel on the assumption that the gel expanded uniformly without changing its volume upon compression. In cases when the initial Young’s modulus was calculated from the thus-corrected area for some food gels, the linearity was increased for a wider range of strain. 相似文献