全文获取类型
收费全文 | 1402篇 |
免费 | 119篇 |
国内免费 | 132篇 |
专业分类
1653篇 |
出版年
2024年 | 4篇 |
2023年 | 32篇 |
2022年 | 35篇 |
2021年 | 52篇 |
2020年 | 47篇 |
2019年 | 48篇 |
2018年 | 35篇 |
2017年 | 58篇 |
2016年 | 51篇 |
2015年 | 52篇 |
2014年 | 76篇 |
2013年 | 88篇 |
2012年 | 77篇 |
2011年 | 75篇 |
2010年 | 57篇 |
2009年 | 60篇 |
2008年 | 69篇 |
2007年 | 98篇 |
2006年 | 66篇 |
2005年 | 71篇 |
2004年 | 62篇 |
2003年 | 37篇 |
2002年 | 41篇 |
2001年 | 40篇 |
2000年 | 27篇 |
1999年 | 30篇 |
1998年 | 34篇 |
1997年 | 22篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 29篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 21篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有1653条查询结果,搜索用时 0 毫秒
201.
1. Time perception is seldom studied in invertebrates, with the limited experimental evidence being insufficient to provide a comprehensive pattern of the capacity of invertebrates to measure time and use it in decision‐making processes. 2. In this study, it was hypothesized that insect parasitoids have evolved the capacity to measure time precisely and to use it to optimize foraging decisions related to host exploitation. To examine time perception in females of the gregarious egg parasitoid Trichogramma euproctidis, the present study used their ability to adjust their investment (number of eggs laid) in a host to the initial transit duration (interval between the first contact with the host and the following contact with the substrate). Females utilize this method to assess host egg size, as a large egg necessarily requires more time to evaluate than a small host. In this study, the initial transit duration for a given sized egg was artificially extended by suspending it. 3. For similar sized hosts, female T. euproctidis significantly increased both oviposition duration and progeny allocation following a longer initial transit duration. 4. These results demonstrate the intrinsic capacity of this parasitoid to measure time and to adjust their progeny investment accordingly. This is believed to be one of the few demonstrations of a retrospective measure of time in an invertebrate. 相似文献
202.
203.
Anja J. Engel Steffen Paech Markus Langhans James L. van Etten Anna Moroni Gerhard Thiel Oliver Rauh 《Traffic (Copenhagen, Denmark)》2023,24(11):533-545
When the K+ channel-like protein Kesv from Ectocarpus siliculosus virus 1 is heterologously expressed in mammalian cells, it is sorted to the mitochondria. This targeting can be redirected to the endoplasmic reticulum (ER) by altering the codon usage in distinct regions of the gene or by inserting a triplet of hydrophobic amino acids (AAs) into the protein's C-terminal transmembrane domain (ct-TMD). Systematic variations in the flavor of the inserted AAs and/or its codon usage show that a positive charge in the inserted AA triplet alone serves as strong signal for mitochondria sorting. In cases of neutral AA triplets, mitochondria sorting are favored by a combination of hydrophilic AAs and rarely used codons; sorting to the ER exhibits the inverse dependency. This propensity for ER sorting is particularly high when a common codon follows a rarer one in the AA triplet; mitochondria sorting in contrast is supported by codon uniformity. Since parameters like positive charge, hydrophobic AAs, and common codons are known to facilitate elongation of nascent proteins in the ribosome the data suggest a mechanism in which local changes in elongation velocity and co-translational folding in the ct-TMD influence intracellular protein sorting. 相似文献
204.
Sara Hintze Jason R. Yee 《Biological reviews of the Cambridge Philosophical Society》2023,98(3):792-806
The concept of flow, a state of complete absorption in an intrinsically rewarding activity, has played a pivotal role in advancing notions of human well-being beyond minimising suffering towards promoting flourishing and thriving. While flow has played a fundamental role in human positive psychology, it has not yet been explored in non-human animals, leaving an enormous void in our understanding of intrinsic motivation in animals. As ethology and related fields keep progressing in uncovering complex cognitive and affective capacities of non-human animals, we propose the time is ripe to translate the concept of flow to animals. We start by embedding flow in the topic of intrinsic motivation and describe its impact on positive human psychology and potentially positive animal welfare. We then disambiguate flow from related concepts discussed in the animal literature. Next, we derive experimental approaches in animals from the canonical characteristics of flow in humans and provide guidelines for both inducing and assessing flow by focusing on two characteristics that do not necessarily depend on self-report, namely resistance to distraction and time distortion. Not all aspects of the human flow experience are (yet) translatable, but those that are may improve quality of life in captive non-human animals. 相似文献
205.
206.
H. J. Barclay J. W. Hargrove P. van den Driessche 《Medical and veterinary entomology》2020,34(2):151-163
A population model for tsetse species was used to assess the optimal number and spacing of airborne sprays to reduce or eradicate a tsetse population. It was found that the optimal spray spacing was determined by the time (days) from adult emergence to the first larviposition and, for safety, spacing was assigned to that duration minus 2 days. If sprays killed all adults, then the number of sprays required for eradication is determined by a simple formula. If spray efficiency is less than 100% kill per spray, then a simulation was used to determine the optimal number, which was strongly affected by spray efficiency, mean daily temperature, pupal duration, age to first larviposition and the acceptance threshold for control, rather than eradication. For eradication, it is necessary to have a spray efficiency of greater than 99.9% to avoid requiring an excessive number of sprays. Output from the simulation was compared with the results of two aerial spraying campaigns against tsetse and a least squares analysis estimated that, in both cases, the kill efficiency of the sprays was not significantly less than 100%. 相似文献
207.
Habibollah Faraji Mohammad Ramezani Baratali Mashkani Hamid R. Sadeghnia Hamid M. Benhangi Saeed Hosseini Teshnizi Fatemeh Soltani 《Biotechnology progress》2019,35(4):e2819
Staphylokinase (SAK) is a promising thrombolytic agent for the treatment of patients suffering from blood-clotting disorders. To increase the potency of SAK and to minimize vessel reocclusion, a new construct bearing SAK motif fused to tsetse thrombin inhibitor (TTI) via a 20-amino acid linker with 2 RGD (2 × arginine-glycine-aspartic acid inhibiting platelet aggregation via attachment to integrin receptors of platelet) was codon optimized and expressed comparatively in Pichia pastoris GS115 as a Mut+ strain and KM71H as a Muts strain. Fusion protein was optimized in terms of best expression condition and fibrinolytic activity and compared with the rSAK. Expression level of the designed construct reached up to 175 mg/L of the culture medium after 72-hr stimulation with 2.5% methanol and remained steady for 3–4 days. The highest expression was obtained at the range of 2–3% methanol. The SAK-2RGD-TT (relative activity >82%) was more active at 25–37 °C than rSAK (relative activity of 93%). Further, it showed relative activity >80% at pH ranges of 7–9. Western blot analysis showed two bands of nearly 27 and 24 kDa at ratio of 5 to 3, respectively. The specific fibrinolytic activity of the SAK-2RGD-TTI was measured as 8,269 U/mg, and 19,616 U/mg for the nonpurified and purified proteins, respectively. Deglycosylation by using tunicamycin in culture medium resulted in higher fibrinolytic activity of SAK-2RGD-TTI (2.2 fold). Consequently, compared to the rSAK, at the same equimolar proportion, addition of RGD and TTI fragments could increase fibrinolytic activity. Also, P. pastoris can be considered as an efficient host for overexpression of the soluble SAK-2RGD-TTI with high activity without requiring a complicated purification procedure. 相似文献
208.
209.
ERIC A. ODELL FRANCES M. PUSATERI GARY C. WHITE 《The Journal of wildlife management》2008,72(6):1311-1317
Abstract: Black-tailed prairie dogs (Cynomys ludovicianus) are a species of concern and accurate estimates of occupied area are required to assess their status. We conducted aerial line-intercept surveys to estimate colony areas in Colorado, USA, 2006–2007. Optimal allocation based on results from a previous (2002) survey was used to distribute flight time to sample 28 counties. Uncorrected estimates of active and inactive colony areas from the aerial surveys were 329,529 (SE=16,841) ha and 18,292 (SE=2,366) ha, respectively. We attempted to ground-truth a randomly selected sample of 186 colony intercepts but gained complete access to only 150. Ground-truthing demonstrated that aerial surveys estimated only 96% of the true lengths of colony intercepts but overestimated the proportion of active colonies. Corrected estimates of active and inactive colony areas are 319,165 (SE = 20,105) ha and 42,422 (SE = 11,485) ha, respectively. Because ground-truthing was not conducted in the original 2002 survey, uncorrected estimates from this survey are the appropriate metric to be used for comparison to the 2002 data. Our estimates demonstrated a 29% increase (SE = 6.3) in area occupied since surveys were conducted in 2002. These results are useful to state and federal agencies and other conservation partners in determining the condition of the species when conducting status reviews. 相似文献
210.
DNA复制是一个不对称的过程。不对称的一个体现是复制链分为前导链和滞后链,前者连续复制而后者的复制却不连续。这种不对称最终导致两条链上核酸组成的不对称。链特异的核酸组成偏差最先发现于棘皮类动物和脊椎动物的线粒体DNA上。随着全基因组的大量测序,越来越多的细菌被发现具有类似的链特异的核酸组成偏差,甚至很多真核生物的染色体基因组也被发现具有类似偏差。在某些细菌中,链特异的组成偏差强烈到足以使前导链和滞后链的基因间具有分离的密码子使用。至今,共有11种细菌被发现具有和复制相关的分离的密码子使用。这11种细菌无一例外都属于专性寄生(共生)菌。对于链组成偏差产生的内在机制以及特定细菌具有强烈链组成偏差的成因,目前学术界尚没有统一的理论解释。文章对这一遗传学及基因组学的重要问题进行了综述和展望。 相似文献